I don’t know if he tomorrow. If he , I’ll meet him.
| A．will come; comes | B．comes; comes |
| C．will come; will come | D．comes; will come |
We won’t put off our plan __________ it snows heavily tomorrow.
| A．whether | B．unless |
| C．because | D．While |
______ he talked with her for a long time, he failed to convince(说服)her.
| A．Though | B．But | C．Since | D．As |
Take a map with you while traveling ________ you have a guide or know the city well．
| A．since | B．if | C．unless | D．because |
- The air pollution is terrible.
- It will be worse ________ we take action to protect the environment.
| A．if | B．unless | C．until | D．when |