要配制成含盐为12%的盐水800克，现在已有了含盐10%的盐水240克了，然后再加入一定量的含盐15%的盐水以及一定量的水。那么所加入的一定量的水为多少克( )
A．200克
B．100克
C．80克
D．60克
参考答案：C
解析： 800克含盐为12%的盐水中盐的质量为800×12%=96(克)，现在已有的240克含盐10%的盐水中盐的质量为240×10%=24(克)，那么还需盐96-24=72(克)，所以应加入的含盐15%的盐水的质量为72÷15%=480(克)，那么加入的水的质量为800-240-480=80(克)。故本题选C。
Nowadaysmoreandmorepeopleareconcernedabouttheir health,buthowtokeephealthy? Differentpeoplemay give differentanswerstothisquestion.Inmyopinion, itisessentialto dothe following. First,itisabsolutelynecessarytotakesomeexerciseatregular timeeveryday.Researchshows thatgettingplentyofexercisecanmaketheheartbeatfaster andthelungsworkharder.This strengthenstheheart,reducesthechanceofheartattack,andhelpslower bloodpressure.That’s whymore andmorepeoplearebecomingactive invariouskindsofsportsandexercise.Every morningmanypeople get upearly and takemuchexercise.Some play ballgameswhileothersrun, jog,walkor dancetomusic.Intheafternoon,therearealsomanypeoplekeenonsports.Through sports and exercise, people become healthierand stronger. Medicalresearchers have proved that what people eataffects theirhealth.Theyadvise peopleto eatmorefruitandvegetablesandless meatsuchas beefandporkbecausemeatcontainsmorefat thanpoultry(家禽) and fish. Fat can build up in the arteries(动脉),blocktheflowof blood,and cause a heart attack orstroke（中风）. Gettingridofbadhabitslikesmokinganddrinkingalcoholisalsoanimportantwaytokeep healthy.Smokinganddrinkingalcoholinjureone’shealthagreatdeal,andthereforeshouldbegiven up. Unfortunately few people follow this advice.
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