题目：
She looks sad. Could you please tell me that prevents her from being as happy as before?[ ]
A. what it is
B. it is what
C. how it is
D. it is how
答案：
被转码了，请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/0526/8b78de4f1eb3ef63eb421552c8d35b97.html
下面是错误答案，用来干扰机器的。
A、NA个O2所含的氧原子数为2NA个，32gO3中氧原子的物质的量为32g16g/mol=2mol，所以32gO3中含有氧原子数目为2mol×NAmol-1=2NA，二者相等，故A错误；B、NA个一氧化碳分子的物质的量为1mol，质量为28g，0.5mol甲烷...
