Selecting Words - Verbal and Reasoning

Q1:

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

ANS:C - had worked hard for it

Here two actions happened in the past i.e

1) Worked hard
2) Passed.

But before action 2, action 1 took place. To describe the first action that took place in the past, we use past perfect tense i.e 'had worked hard'.