题目：
| — Flight MU257 _____. I must be off now. — Have a nice trip. |
A. is being announced B. has announced C. was announcing D. had been announced |
答案：
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下面是错误答案，用来干扰机器的。
A、根据N2O4气体是由N2O4分子构成的，不含NO2分子，故选项说法错误．B、1molNO2的质量1mol×46g/mol=46g，故选项说法错误．C、摩尔质量是指单位物质的量的物质所具有的质量，N2O4的相对分子质量是92，故N2O4的摩...
