—How much shall I pay for the phone call?
—You________. This is free of charge.
| A．shouldn't | B．can't | C．don't have to | D．mustn't |
Willie's wife never gives him pocket money until he __________ clearly how he will spend it.
| A．has explained | B．explained |
| C．will explain | D．is to explain |
Can you explain __________ the sun goes down in the west?
| A．why is it that | B．why it is that |
| C．how it is that | D．how is it that |
What an unforgettable experience ！ I'll write it down __________ it is still fresh in my memory.
| A．since | B．while |
| C．after | D．until |
__________，many people go in for them and benefit from them.
| A．However some sports are challenging |
| B．However challenging some sports are |
| C．No matter how challenging are some sports |
| D．No matter how some sports are challenging |
Although __________ to be the best in a recent science competition, the students remain hard-working.
| A．judged | B．judging |
| C．judge | D．having judged |