分子的偶极矩有方向性,非极性分子的偶极矩不为0（）
Many of O. Henry’s stories tell about the lives of poor people in _____.
_________ are stories about people’s problem.Sometimes they are romantic and sentimental.Sometimes they are sad and depressing.
执行实时平移命令,光标显示为____,按住鼠标左键拖动即可实时平移图形
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