This question tests your understanding of conditional sentences in English grammar, specifically the use of subjunctive mood for hypothetical situations. Here is the step-by-step explanation:
Thus, the correct answer is option (a), where "was" should be replaced with "were" to form the correct hypothetical condition.
Unless you do not listen to his advice, (a) I am not going (b) to help you. (c) No error (d)
The teacher called Ravi (a)and asked him (b) to describe about the incident. (c) No error (d)