问题标题：
【Poolexpertshavedetermindedtheproperlevelsofchemicalsthatmust-------inpoolwatertoprotecttheswimmersfrominfectionandtheequipment-------corrosionanddamage.Chlorinekeillsharmfulorganisms,butitwon'tworkproperlyifthealkalin】
问题描述：
Poolexpertshavedetermindedtheproperlevelsofchemicalsthatmust-------inpoolwatertoprotecttheswimmersfrominfectionandtheequipment-------corrosionanddamage.Chlorinekeillsharmfulorganisms,butitwon'tworkproperlyifthealkalintyofthewateristoo----.Ifthecalciumcontentofthewaterisinadequate,thewaterwillleachcalciumfromthewallsofthepool,------them
1.A.maintainB.bemaintainedC.havemaintainedD.bemaintaning
2.A.byB,fromC.forD.of
3.A.lowB.belowC.underD.beneath
4.A.haveweakenedB.isweakeningC.weakeningD.weakens
郎非回答：
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.andtheequipment-------corrosionanddamage与前一短语toprotectthesw...
点击显示
英语推荐
热门英语推荐