If you want to have a good mastery of knowledge, you must ________ what you are being taught in class and make immediate use of it．

depend on

decide on

concentrate on

keep on

When he climbed a tall tree to save a little girl, he risked ________ off it and ________ his legs, but he landed safe in the end．

falling; breaking

to fall; break

falling; break

to fall; broke

________, we were so poor that we couldn’t afford to buy a color TV set, so every evening, we had to go to bed very early．

At times

At the same

At a time

At one time

________ the development of modern medicine, human beings expect to live much longer．

In

With

Under

During

They don’t allow _______ here．That is to say, we are not allowed _______ here．

to smoke; to smoke

smoking; smoking

to smoke; smoking

smoking; to smoke

I remember his telephone number is 8666888,but you’d better ________．

be sure

make sure

find out

look out

The money collected from ticket sales could be _______ food and clothes for the people in the flooded areas．

cost

paid off

spent on

paid back

Apples are usually sold by _______ weight, and eggs are sometimes sold by _______ dozen．

the; the

/; a

/; the

the; a

I have never dined with you, sir; and I see no reason ________．

how can I know

how I ought to know

why shall I know

why I should know

Our educational system must prepare our citizens to be persons who have respect for nature _______ for mankind and persons who want to enrich the world．

as well as

such a

the same as

as to