David didn’t give up ______ he had failed in the experiment four times．
| A．if | B．while | C．though | D．since |
---How will you go to the zoo tomorrow?
---If it ______ tomorrow, I’ll go there by car．
| A．raining | B．rain | C．rains | D．will rain |
While Helen ________ the piano，her mother came in．
| A．was playing | B．is playing | C．played | D．plays |
The shorts are _________ of all, but they are _________．
| A．best, cheaper | B．better, dear |
| C．the best，dear | D．good, cheap |
The room was dark，_________ I turned on the lights．
| A．and | B．or | C．but | D．so |
----________ have you been studying at school?
----For more than four years．
| A．How often | B．How long | C．How old | D．How far |