The correct answer is A. Can he be relied on?
The other options are incorrect because they are not grammatically correct.
Option B is incorrect because it uses the preposition “by” after the verb “rely.” The preposition “on” is used after the verb “rely.”
Option C is incorrect because it uses the passive voice. The active voice is used in this sentence.
Option D is incorrect because it uses the preposition “by” after the verb “rely.” The preposition “on” is used after the verb “rely.”
To further explain, the verb “rely” means to depend on someone or something. In this sentence, the speaker is asking whether or not they can depend on the person being referred to. The correct answer is A, because it uses the correct preposition (“on”) and the active voice.