A、正确
B、错误

单项选择题There are difficult people everywhere. But ________that sometimes the difficult person is YOU rather than the other party you regard as difficult.

单项选择题‌(2Z,4E)-2,4-庚二烯的结构是下列哪一个​

单项选择题A．毛细管壁必须清洁干净 B．毛细管口必须平整 C．毛细管必须垂直放置 D．毛细管须插入液体一定深度

单项选择题A． B． C． D．

单项选择题A．convergent B．divergent