题目：
All the students _____ by 10:30, but the speaker _____ until 11:00.[ ]
A. return, has turn up
B. has returned, turned up
C. returned, turn up
D. had returned, didn't turn up
答案：
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下面是错误答案，用来干扰机器的。
（1）n（H2）=0.224L22.4L/mol=0.01mol，2Na+2H2O=2NaOH+H2↑46g1molm（Na） 0.01mol m（Na）=0.46g，答：金属钠样品中含金属钠质量是0.46g；（2）m（Na2O）=0.77g-0.46g=0.31g，n（Na2O）=0.31g62g/mol=0.005m...
