Not until the early years of the 19th century ________ what heat was.
| A．man did know | B．did man knew | C．didn't man know | D．did man know |
While _________, people sometimes can’t help buying something they don’t really need.
| A．shopped | B．being shopped | C．to shop | D．shopping |
Alexander tried to get his work ______ in the medical field.
| A．to recognize | B．recognizing | C．recognized | D．recognize |
You __________ buy a gift, but you can if you want to.
| A．must | B．mustn’t | C．have to | D．don’t have to |
John thinks it won’t be long ________ he is ready for his new job.
| A．when | B．after | C．before | D．since |
It was from only a few supplies in the nearby village ______ the hostess cooked such a nice dinner.
| A．where | B．that | C．when | D．which |