Let’s examine the sentence: “He doesn't know anything about cars, so he ____ by a trained mechanic.” The sentence has two clauses joined by ‘so.’ The first clause states that ‘he’ has no knowledge about cars and implies that ‘he’ cannot repair it. The second clause talks about ‘a trained mechanic’ and we can easily assume from the facts given that ‘he’ must be taking the help of a trained mechanic to repair his car. Let’s study the options with this understanding. Option A cannot be used as it would mean ‘he’ repairs it himself and this is wrong. Option B cannot be used as ‘it’ cannot come immediately after ‘he.’ Option D cannot be used as it would mean that ‘he’ and not the car ‘is repaired.’ Also, Options A, B and D would make the sentence meaningless. So, Option C is the correct answer that brings out the intended meaning of the sentence.