I didn’t pay attention to the teacher. I failed to...

Câu hỏi: I didn’t pay attention to the teacher. I failed to understand the lesson.

A. Although I paid attention to the teacher, I failed to understand the lesson.

B. I would have understood the lesson if I had failed to pay attention to the teacher.

C. I would have understood the lesson if I had paid attention to the teacher.

D. Unless I failed to understand the lesson, I would pay attention to the teacher.