题目

下列叙述中正确的是                                          A．摩尔是物质的质量的单位             B．碳的摩尔质量为12g C．阿伏加德罗常数约为6.02×1023mol-1     D．一个碳原子的质量为12g 答案：COur teacher walked into the classroom _______ a smile _______ his face.A. for; on B. of; in C. with; on D. has; on