1.The twins have been working on a science project all semester.
^^^^
It's taking a lot of time.
請問它這裡用have,是不是因為後面的" It is"
如果它後面是 " It was",前面是不是用 had?!
2.Oh, no! I ______ my passport! It's not in my bag.
請問,我很確定我的passport在我翻包包之前不見了,但不知道於過去何時不見?!
這要用 lost/ have lost ?!
3.請問是不是只要知道先後順序,就沒有一定要用had p.p./had been Ving ?!