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

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

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

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