Mark the letter A, B, C or D on...

Câu hỏi: Mark the letter A, B, C or D on your answer sheet to indicate the sentences that combines each pair of sentences in the following questions.

A. It was because his overconfidence that ruined our plan completely

B. He was overconfident, which ruined our plan completely

C. That he was overconfidence ruined our plan completely

D. It was his overconfidence ruined our plan completely.