He passed the examination in the first class because he …… A. was hard working for it B. worked hardly for it C. had worked hard for it D. was working hard for it

The correct answer is C. He had worked hard for it.

The other options are incorrect because they do not express the idea that the person had worked hard in the past.

• Option A: “was hard working for it” is incorrect because it uses the present continuous tense, which indicates that the person was working hard at the time of speaking. However, the question is about why the person passed the examination in the past, so we need to use a past tense verb.
• Option B: “worked hardly for it” is incorrect because it uses the adverb “hardly,” which means “almost not at all.” This does not make sense in the context of the question, since we are told that the person passed the examination in the first class.
• Option D: “was working hard for it” is incorrect because it is the same as option A, except that it uses the past progressive tense instead of the present progressive tense. As explained above, we need to use a past tense verb in order to express the idea that the person had worked hard in the past.

Therefore, the correct answer is C. He had worked hard for it.