阅读理解，选择正确的答案。

    April Fools'Day is a day to play jokes on others．No one knows how it began，but people think it first began in France．

    Each country celebrates April Fools'Day differently．In France，people call the April fools "April Fish"．They tape a paper fish to their friends' backs to fool them．When he or she finds this，they shout” April Fish!”

    In the UK，people play jokes only in the morning．You are a“noodle”if someone fools you．

    In the US，people play small jokes on their friends on the first of April．They may point down to your shoe and say，“Your shoelace iS untied．”If you believe them and look down，you are an April fool then．

按要求做题。

a．除去石灰水中悬浮的碳酸钙颗粒____；

b．除去氯化钠中混有的碘单质（碘易由固态变为气态）____；

c．分离水与苯的混合物____；

d．分离氯化钠和硝酸钾的混合物____．