Enforcing distributed and one-to-one meaning

Question

Does the object of the plural subjects in the following sentences also need to be plural?

1a. The kids need to complete their personal collage for homework.

1b. The student drivers couldn't figure out how to start their car.

or

2a. The kids need to complete their personal collages for homework.

2b. The student drivers couldn't figure out how to start their cars.

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All of the above sentences are ambiguous. The subjects from the first pair could all be sharing the same object, the personal collage or car, and the subjects from the second pair could each have more than one of the object. Im wondering how I could construct a sentence where it's clear that each subject has just one of the object and is not open to misinterpretation.

Answer 1

OP writes: I'm wondering how I could construct a sentence that means each subject has just one of the object without being open to misinterpretation.

Each of the students needs to complete his or her homework.

None of the student drivers could figure out how to start his or her car.

You can substitute their for his or her.

There is always some potential for ambiguity when using pronouns. Context normally makes things clear.

Answer 2

This quandary always arises in statements of this kind. The statements are ambiguous although their sense is widely understood. Only in polygamous societies could the following sentence be interpreted to mean that a man might have more than one wife.

Men should escort their wives up the steps.

If you want to avoid any such ambiguity entirely, you need to write:

Each kid should complete his/her/their collage.....

No student driver could figure out how to start his/her/their/a car.

It's seldom that it's necessary to be so precise. In everyday writing and conversation, the meaning of sentences like:

Sons should precede their fathers into the hall

are difficult to misinterpret except by the most obtuse. But if in doubt, you have to resort to spelling things out.