Writing Multiple-Choice Questions
Pronoun/Number Agreement

Did everyone remember to bring their permission slip with them?

The question above is grammatically incorrect.
Everyone is singular, strange as that may seem, and refers to a collection of people. It also refers to each individual in a collection of people—everyone.
To highlight this error, substitute the equivalent phrase each of you into the permission slip sentence:

Did each of you remember to bring their permission slip with them?

The pronoun their is plural, but it refers back to a singular subject, each of you—or, in the previous sentence, everyone. The proper form is:

Did everyone remember to bring his or her permission slip with him or her?

Yes, this is cumbersome, but correct.
The following words behave just like everyone: anyone, no one, nobody, every, and each.
On another topic, check out this sentence:

Acme Widgets reported today that their earnings had fallen sharply.

Widgets may be plural, but presumably there is only one company called Acme Widgets. If it’s a single company, it requires a singular pronoun:

Acme Widgets reported today that its earnings had fallen sharply.

Anytime you see a plural pronoun in a Writing item, check the noun or pronoun it refers to and replaces (its antecedent) to see whether this very common error is being tested.
Watch out for “pronoun shift” too:
  • Incorrect If you start with a particular pronoun, one shouldn’t shift to another later on in the sentence.
  • Correct So, if one would like to do as well as one can on the SAT, keep this commonly tested error in mind.
  • Correct That way, you will be happy with the score you receive.
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