The pressure _____ causes Americans to be energetic, but it also puts them under a constant emotional strain (过度紧张).
Excuse me, but can you tell me________.
The number of the people in the room_______sixty, but a number of them_________students.
What did he say? I don’t know what________.
I told your friend how to get to the hotel, but perhaps I______have driven her here.
I’m sorry to have hurt you, but I didn’t do it________.