Question

principal said all the student have passed change into indirect

Answer 1

they were told by the principal that all the students had pased.
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Answer 2

They were told by the principal that all the students had passed. When direct to indirect sentence, the meaning should be same but speech is different.

The tense of words inside are quotation and changed into past tense.

Direct speech exercises with answers are so helpful and thus get meaning by changing the sentences.