皮皮学，免费搜题
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【简答题】
Choose the proper response to the question. (根据问句选择正确的答语) ( )1.What is it? ( )2.Did your teacher give you any advice? ( )3.What advice? ( )4.What do you do with your spelling? ( )5.How about your grammar and vocabulary? A.Yes,he did. B.About speaking more English in class or after class. C.Oh,I always practise doing more reading and more exercises about them. D.It's my English study plan，I am going to work hard this year. E.I always check my spelling with a dictionary.
拍照语音搜题，微信中搜索"皮皮学"使用
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参考解析：
知识点：
皮皮学刷刷变学霸
举一反三
【多选题】在质点系中,以下描述中哪几项是正确的?( )
A.
一对相互作用力的功之和与参考系无关
B.
一对相互作用力的功之和不一定为零
C.
一对滑动摩擦力的功之和为负
D.
一对正压力的功之和不一定为零