Select the correct passive form of the given sentence.

Conduct all the exams in a fair and proper manner.

Let all the exams be conducted in a fair and proper manner.

The correct passive form of the given sentence is Let all the exams be conducted in a fair and proper manner.

The active voice of the sentence is Conduct all the exams in a fair and proper manner. This sentence is in the imperative mood, which is used to give commands or make requests. The passive voice of the sentence is formed by putting the subject of the active sentence after the verb "to be" and the past participle of the main verb. In this case, the subject of the active sentence is "all the exams" and the main verb is "conduct." The past participle of "conduct" is "conducted." So, the passive form of the sentence is Let all the exams be conducted in a fair and proper manner.

The other options are incorrect because:

• The exams were all conducted in a fair and proper manner. is in the simple past tense, while the original sentence is in the imperative mood.
• All the exams are conducted in a fair and proper manner. is in the present tense, while the original sentence is in the imperative mood.
• Let all exams should be conducted in fair and proper manner. is grammatically incorrect. The verb "should" should not be used with the past participle of the verb "conduct."