Although the causes of cancer_____, we do not yet have any practical way to prevent it.
| A．are being uncovered | B．have been uncovering | C．are uncovering | D．have uncovered |
Susan and I can go to the lecture ___.
| A．but neither can Charles | B．and so Charies can |
| C．but Charles can’t | D．and Charles also can |
Joan___play on Saturday.
| A．going to | B．can | C．is going | D．can to |
Tell the boy that he ___ in the river.
| A．swims | B．swim | C．swimming | D．to swim |
You___hand it in at once, you may hand it in tomorrow.
| A． needn't | B．may not | C． can't | D．must not |
Anne___tomorrow.
| A．can sing | B．can to sing | C．is going sing | D．going to sing |