题目

The boy is only five years old, but he is quite used          the telephone.   A. to answer     B. to answering     C. of answering    D. by answering 答案：B同位素示踪法可用于反应机理的研究，下列反应或转化中同位素示踪表示正确的是（　  　） A．2Na218O2 + 2H2O == 4Nal8OH + O2↑ B．NH4Cl + 2H2ONH3·2H2O + HCl C．2KMnO4 + 5H218O2 + 3H2SO4 == K2SO4 + 2MnSO4 + 518O2↑+ 8H2O D．K37ClO3 + 6HCl == K37Cl + 3Cl2↑+ 3H2O