Question

英语问题!!!!急！！！求高人啊！谢谢！！！！1

Pool experts have determinded the proper levels of chemicals that must-------in pool water to protect the swimmers from infection and the equipment-------corrosion and damage.Chlorine keills harmful organisms,but it won't work properly if the alkalinty of the water is too----.If the calcium content of the water is inadequate,the water will leach calcium from the walls of the pool,------them
1.A.maintain B.be maintained C.have maintained D.be maintaning
2.A.by B,from C.for D.of
3.A.low B.below C.under D.beneath
4.A.have weakened B.is weakening C.weakening D.weakens

Answer 1

1.选B。 这里是一般的情况。maitain维持，保持。游泳池中的学药品的含量必须保持在一个恰当的水平。在这里要用被动语态，是人类保持其含量。
2.选B。 and the equipment-------corrosion and damage与前一短语to protect the swimmers from infection 结构是一样的，只不过是省略了一些相同的词而已。
3.选A。如果水中碱的浓度太低，它就不起作用了。
4.选C。表示伴随动作。

Answer 2

BBAC

Answer 3

BBAC