题目

已知自然界氧原子有3种16O、17O、18O，氢原子有2种H、D，从水分子的组成来看，自然界的水一共有A. 3种           B. 6种          C. 9种          D. 12种  答案：C解析:  It is the third time that Susan ______ late to work and it’s high time that she ________the truth.A．has come; tell B．has come; toldC．came; should comeD．had come; told