Complete the sentence. Write forms of the verbs, use the comma (..., ...). The air
(be) cleaner if people
(use) less cars.

To complete the sentence, we need to use the correct forms of the verbs "be" and "use" and add a comma between them. The sentence is: "The air (be) cleaner if people (use) less cars."

Let's break it down step by step:

1. Determine the correct form of the verb "be" in the first part of the sentence. The subject "air" is singular, so we need to use the third person singular form of "be," which is "is." Therefore, the first part becomes "The air is..."

2. Now, let's move on to the second part of the sentence. We need to determine the correct form of the verb "use" for the subject "people." Since we are talking about a hypothetical or conditional situation, we need to use the simple present subjunctive form of "use," which is "use." Therefore, the second part becomes "...if people use..."

3. Lastly, we need to add the comma between the two verb forms. The final sentence is: "The air is cleaner if people use less cars."

Let me know if you have any further questions!