This is one of the most missable questions in Standard English Conventions, because on these your ear is working for the test, not for you.
The error pattern: a thing compared to a person
"X is [comparative] than Y" only means something when X and Y are the same kind of thing: both objects, both people, both measurements. The SAT builds sentences where one side is a thing and the other is secretly a category error, an attribute of one item compared against a whole different item.
Read this:
Ravi's paintings are more detailed than Mira.
Sounds normal out loud. Look at what it literally says: Ravi's paintings (things) are more detailed than Mira (a person). A painting is not more detailed than a person; that comparison is nonsense. What the writer meant was Ravi's paintings versus Mira's paintings.
Here is the check, and it takes about ten seconds. Put one word on each side of "than" (or "as"):
- Left of "than": paintings.
- Right of "than": Mira, a person.
Different labels. The comparison is illogical. When the two labels do not match, you have to restore the noun that went missing, and that is exactly what "that of," "those of," and possessives are for. Call it the label test: name each side in one word, and if the words are not the same kind of thing, the sentence is broken.
"That of" and "those of": the number decides
The most common repair the SAT hands you is "that of" or "those of." Both are stand-ins for a noun you already said, so you do not have to repeat it.
- "That of" replaces a singular noun.
- "Those of" replaces a plural noun.
Watch the number:
The population of Denver is larger than that of Boulder.
"That of" equals "the population of." One population, so "that of." The comparison is now population versus population. Clean.
Austen's novels are shorter than those of Dickens.
"Those of" equals "the novels of." Novels is plural, so "those of." Now it is novels versus novels, not novels versus a person.
The only decision is number. Ask what noun is being repeated, and ask whether it is one thing or many. One thing points to "that of." Many things point to "those of." The SAT loves to offer you the wrong-number version as a distractor, so this is worth being deliberate about.
Possessive fixes: let the apostrophe carry the noun
Often the cleaner fix is a possessive, and the SAT will offer it as the right answer while burying "that of" as a slightly-too-wordy option, or the reverse. Both can be grammatical; you are choosing the one that actually fits the sentence.
A possessive noun carries the repeated noun on its back:
Ravi's paintings are more detailed than Mira's.
Mira's what? Paintings. The apostrophe does the work, no repetition needed. Same move here:
A cheetah's top speed exceeds a greyhound's.
Greyhound's top speed. The possessive restores the second "top speed" so you are comparing speed to speed, not speed to a dog.
If the apostrophe mechanics feel shaky (its versus it's, singular versus plural possessive), that is a separate rule worth locking down first; see the guide on apostrophe rules. The comparison fix and the possessive fix meet right here: you cannot confidently write "than Mira's" if you are not sure where the apostrophe goes.
Like vs. as: the second comparison trap
The same domain hides a second trap: "like" versus "as." They are not interchangeable, and the SAT tests the boundary.
- "Like" compares nouns. It takes a noun, not a clause. "Like her sister, Dana runs marathons."
- "As" introduces a clause, a group of words with its own verb. "As I mentioned, the deadline moved."
The trap is using "like" in front of a clause:
Like I said, the results held up.
There is a verb ("said") after "like," which means "like" is wrong; it should be "as." Quick test: look at what comes right after the word. A verb is coming, use "as." Just a noun, use "like."
This connects to a bigger idea the test rewards: parallel structure, keeping the two halves of a comparison in the same grammatical shape. If comparisons and parallelism both trip you, the guide on parallel structure covers the pattern sitting underneath both.
Run the check on real sentences
Here is a short set. Cover the fix, run the label test yourself, then check.
The winters in Minnesota are colder than Georgia.
Winters (a thing) versus Georgia (a place). Mismatch. Fix: "colder than those of Georgia" or "colder than Georgia's." Winters is plural, so "those of."
This year's revenue grew faster than last year.
Revenue (a thing) versus last year (a time). Mismatch. Fix: "faster than that of last year" or, cleaner, "faster than last year's."
The bee's wingbeat is quicker than a hummingbird.
Wingbeat versus a bird. Mismatch. Fix: "quicker than a hummingbird's" or "than that of a hummingbird."
Notice the pattern: every fix reintroduces the dropped noun, either through "that of," through "those of," or through an apostrophe. Predict the fix in your own words before you look at the answer choices, so the smooth-sounding wrong options cannot anchor you into the version that merely reads well.
The self-test you can run today
On your next Conventions set, every time you see "than" or "as," stop before reading the choices and put one word on each side. If the two words are not the same kind of thing, you already know the answer has to add "that of," "those of," or a possessive, and you know which one from the number. Deciding before you peek is the anti-anchoring habit that keeps the smooth-sounding trap from talking you out of the right fix (more on that in the guide on answer anchoring, and the commit-first move in predict-then-peek).
If you miss one of these and could fix it instantly the next day, that is not a knowledge gap, it is a leak: your ear overriding a rule you already know. Name it, and catch yourself in the act next time.
Practice it now: the free simplesat grammar drill runs Standard English Conventions with per-trap feedback, so you see the label mismatch called out the moment you miss it. No signup, works as a guest: /?drill=grammar-conventions