________ you have made a promise, you should carry it out．

A．Until

B．Once

C．For

D．As soon as

I can't afford ________ a new camera without ________ my old one．

A．buy; sell

B．to buy; to sell

C．buying; selling

D．to buy; selling

On my present salary, I just can't ________ a car which costs over 3000 pounds．

A．allow

B．afford

C．get

D．demand

I hear your new boss is not easy ________, so you will have to be more careful．

A．to get along with

B．to get along

C．to be got along with

D．to be got along

We are flying ________ 20,000 feet．I feel very nervous．

A．at altitude of

B．at an altitude of

C．at the height of

D．at an altitude

The oxygen equipment made it possible for the climbers to rest and sleep at very high ________．

A．level

B．heights

C．altitudes

D．atmosphere

When we ________ after a long talk, we found the children sleeping in ________ beds．

A．separated; separate

B．separated; separated

C．separate; separate

D．separate; separated

Sorry to have taken your umbrella by mistake．It's because my chair is ________ to yours．

A．similar

B．same

C．the same as

D．different

They did not find ________ to prepare for the worst conditions they might meet．

A．worth

B．worthwhile

C．it worth

D．it worthwhile

These problems are worth ________．

A．to pay attention

B．to pay attention to

C．paying attention

D．paying attention to