1. We were tired because we had driven for two hours.
for two hours là dấu hiệu câu quá khứ hoàn thành .
Công thức thì quá khứ hoàn thành : S + had + Ved/PII
2. Anna had never been stopping studying all day. She didn’t even have one break.
Công thức : S + had been + Ving + all day : Ai đó đã làm gì suốt ngày.