33．Only after he had spent several nights working on the math problem_______to wonder whether the problem was wrongly set．
| A．did he begin | B．he began | C．he did begin | D．began he |
---John and Tom, you two clean the classroom today, _____?
---But we cleaned it yesterday.
| A．do you | B．will you | C．didn’t you | D．don’t you |
Pleasant as they made it ______ in Jiuzhaogou, we felt tired after the long journey.
| A．to travel | B．travel | C．travelled | D．travelling |
Although the police thought he was the most likely one, _____ they had no exact proof about it, they could not arrest him.
| A．when | B．until | C．before | D．since |
As we know, _____ medical examination will help us find out health problems as early as possible.
| A．common | B．general | C．regular | D．normal |
I found some old pictures at the back of my drawer which _____ memories of my childhood.
| A．called in | B．called up | C．called back | D．called for |