题目

甲原子与乙原子的质量比为a：b，而乙原子与碳原子的质量比为c：d，则甲原子的相对原子质量为（ ）            A.                                   B.                                   C.                                   D.  答案：A根据所给提示完成下列句子。（共5小题，每小题2分，计10分）1.人生就是想一场赛跑。你要么领先，要么落后。Life is like a race．You either _____________ or _________________．2.穿红色更容易采取行动。Wearing red can _________________________________________．3.Jim常常怀疑花这么多时间做作业是否值得。Jim often ____________ it is __________ so much time on homework．4.那个小男孩除了躲藏起来，别无选择。That little boy had ________________________________ into hiding．5.让我们惊讶的是，他已经五十多岁了。_______________, he has been in ____________________________．