Reason clause with perfect aspect – choose the correct tense form of "work hard". Base sentence: "He passed the examination in the first class because he _____." Instruction: Select the form that describes an action completed before the result. Final instruction: Choose the grammatically and logically correct option.

Given data

• Outcome in simple past: "He passed."
• Cause must precede the outcome.

Concept/Approach
When one past action is prior to another, use past perfect for the earlier action: "because he had worked hard."

Option analysis
had worked hard for it — correct tense and adverb placement. ✅was hard working for it — incorrect phrase order; hard-working is an adjective, not used here. ❌worked hardly for it — hardly means "scarcely," reversing the meaning. ❌was working hard for it — past progressive; suggests ongoing action, not completed cause. ❌

Final Answer
had worked hard for it