The correct answer is OPTION 1- The students were made to laugh.

The correct passive form of the given sentence is: The students were made to laugh.

1. The students were made to laugh. (Correct) This sentence correctly uses the passive voice and conveys the meaning that someone (not mentioned in the sentence) caused or prompted the students to laugh.

2. The students were made laughing. (Incorrect) This sentence is not in the correct grammatical structure for the passive voice. The correct form would be "The students were made to laugh."

3. She was making students laugh. (Incorrect) This sentence is in the active voice and does not represent the passive form of the original sentence.

4. She was made to laugh by students. (Incorrect) This sentence is in the passive voice, but the meaning is different from the original sentence. It implies that the students made "her" laugh, not the other way around as in the original sentence.