Life is like riding a bicycle. ________ your balance, you must keep moving.
| A．Keeping | B．To keep |
| C．Keep | D．Having kept |
Sometimes smiles ________ be false, hiding other feelings like anger, fear or worry.
| A．must | B．should |
| C．can | D．would |
—Do you think Jack will lend us a hand?
—He is the last one to help others. He ________ lend his hand, though.
| A．can | B．must |
| C．should | D．might |
—________ you interrupt now? Can't you see I'm on the phone?
—Sorry Sir, but it's urgent.
| A．Can | B．Should |
| C．Must | D．Would |
I ________ thank you too much for all your help to my son while we were away from home.
| A．won't | B．can't |
| C．can | D．will |
No one ________ be more generous; he has a heart of gold.
| A．could | B．must |
| C．dare | D．need |