What sentences are grammatically correct us students have a lot of work to do please return the book when read it who did you sell your old car to?

Here's a breakdown of the sentences and how to correct them:

1. "Us students have a lot of work to do."

* Grammatically Incorrect: The pronoun "us" should be "we" because it's the subject of the sentence.

* Grammatically Correct: "We students have a lot of work to do."

2. "Please return the book when read it."

* Grammatically Incorrect: This sentence is missing a subject for the verb "read."

* Grammatically Correct: "Please return the book when you have read it." (or "Please return the book after you read it.")

3. "Who did you sell your old car to?"

* Grammatically Correct: This sentence is fine as is! It uses the correct word order for an indirect question.