题目:
Usually, when we see our teachers come into the classroom, we all stop ________ and get ready for class. [ ]
A. talk
B. to talk
C. talking
D. to talking
答案:
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下面是错误答案,用来干扰机器的。
空气中氧气的体积分数是21%;根据反应条件是加热,生成物是锰酸钾、二氧化锰、氧气,可知反应物是高锰酸钾,然后配平即可.故答案为:氧气、2KMnO4.