题目

While staying in the village, Jack shared whatever he had with the villagers without asking for anything______. A . in return B . in common C . in turn D . in place 答案：A少数不法商贩将煤矸石（矿井下与煤共生一处的石块）破碎后掺在优质煤中高价销售给客户．客户为了防止上当，最恰当的方法是可以检测下述物理量中的（　　）A．密度B．比热C．熔点D．燃烧值