缓冲溶液的选用依据是所需控制的溶液的pH值。

Directions: For each blank in the following passage there are four words or phrases marked A, B, C and D .Fill in each blank with the word or phrase that best fits the context.
Would you send a monkey to do your shopping for you? Sounds very strange, doesn’t it ? But monkeys can be trained to do some wonderful things. Most people know that monkeys are one of  36   cleverest beasts(兽). Scientists have been studying the connection（联系） __37__ monkeys and people for a long time. They have done experiments that test __38__monkeys are able to do simple things.
In one test, a scientist put two monkeys in two cages beside each other. Each cage had a machine. One cage had a machine which gave out water. __39__ had one which gave out food. Each monkey was given _40__ black and white coins. The black coins worked _41_ in the food machine. The white coins worked in the machine with the __42__. After some time, both animals _43__ know which coin worked in which machine.
Then the test was made _44__. The coin s were taken away. The monkey with the water machine was __45_ to have any water for twenty-four hours. The food monkey was prevented from __46_ any food. The next day, the coins were returned to the monkeys. This time, __47__, the monkey with the food machine was given coins for water machine, and the monkey with the water machine was given the coins that worked in the food machine. What did the two __48__ monkeys do? The two clever monkeys __49__ through the bars (栅栏) of their cages and __50_coins with each other.

小题1:	A．man’s B．earth’s C．nation’s D．nature’s

小题2:	A．between B．with C．to D．from

小题3:	A．when B．what C．whether D．as

小题4:	A．The one B．The rest C．Another D．The other

小题5:	A．a piece of B．a bag of C．a little D．scores

小题6:	A．almost B．nearly C．only D．mainly

小题7:	A．water B．food C．monkey D．scientist

小题8:	A．were used to B．used to C．could hardly D．were able to

小题9:	A．harder B．easier C．worse D．newer

小题10:

A．allowed B．not allowed C．asked D．drank

小题11:

A．wasting B．drinking C．having D．asking

小题12:

A．but B．unless C．however D．although

小题13:

A．tired B．angry C．wild D．poor

小题14:

A．looked B．got C．reached D．arrived

小题15:

A．received B．changed C．refused D．played