.____ at the airport, he telephoned his wife and told her what he would do when he got home.
No one has yet succeeded in solving the _____ of how life first began.
Can you tell me ______?
—She looks very happy. She ______ have passed the exam. --I guess so. It’s not difficult after all.
Mary,along with her parents,______to Paris.
The students were studying in classroom when, all of sudden,the lights went out.