He paid for a seat, when he ______ have entered free.
| A．could | B．would | C．must | D．need |
So difficult it to work out the problem that I decided to ask Tom for advice．
| A．I did find | B．I have found | C．did I find | D．have I found |
The rescue workers were working around the clock, ________ supplies to Yushu Qinghai Province after the earthquake．
| A．to send | B．sending | C．having sent | D．to have sent |
After the earthquake, the first thing the local government did was to provide for the homeless families．
| A．accommodation | B．occupation | C．equipment | D．furniture． |
________ this cake, you'll need 2 eggs, 175 g sugar and 175 g flour．
| A．Having made | B．Make | C．To make | D．Making |
Although the causes of cancer ________, we do not yet have any practical way to prevent it．
| A．have uncovered | B．have been uncovering |
| C．are uncovering | D．are being uncovered |