题目

_____ that he isn’t adequate to the present job, he devotes all his spare time to studyingprofessional knowledge.    A. Concern   B. To concern   C. Concerned   D. Concerning 答案：C下列有关阿伏加德罗常数(NA)的描述正确的是(    ) A.1 mol物质均约含有6.02×1023个分子 B.NA个氢气分子就是1 mol H2 C.1 g氢气约含有6.02×1023个分子 D.NA个12C的质量为12 g