Step 1: Tense rule.
When two actions occur in the past, the earlier action is expressed in past perfect.
Step 2: Checking options.
(A) has complete — grammatically wrong.
(B) will complete — future tense, wrong.
(C) had completed — correct: past perfect for earlier action.
(D) can complete — not suitable.
Step 3: Conclusion.
Correct answer is (C) had completed.