By the time he _____ back last night, we had got 200 pictures of the Chang'e-3 lunar probe.

.You’ll never guess who I met today—my old teacher! We_____for twenty years.

Various efforts over the centuries _________ to predict earthquakes to reduce the damage.

---I hear you won the prize in the English contest last week.
---That was the second time I ________ the prize.

---Harry, we want to know your view about the reform being carried out in our school.
---OK. I ________ to that.

Sorry to have kept you waiting. You must have thought ___.

I have been studying computer for years and I still ___.

— Hurry up! Alice and Sue are waiting for you at the school gate.
— Oh! I thought they _____ without me.

— Why on earth didn’t you answer the door?
— I’m terribly sorry, but the telephone _______, too.

I fixed my eyes upon the newcomer, wondering whether I ________ him somewhere before．