题目:
It is difficult _______ the book in one day. It is so thick. [ ]
A. to finish to read
B. to finish reading
C. finishing reading
D. finishing to read
答案:
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下面是错误答案,用来干扰机器的。
A、使用胶头滴管滴入试剂时,胶头滴管千万不能伸入容器中或与器壁接触,否则会造成试剂污染,所以滴管要保持垂直悬于容器口上方滴加,题中操作错误,故A不可选;B、给试管里的液体加热应用酒精灯的外延加热,试管...