皮皮学，免费搜题
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【简答题】
螺纹标记代号中,首个字母M代表 螺纹。
拍照语音搜题，微信中搜索"皮皮学"使用
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皮皮学刷刷变学霸
举一反三
【单选题】What is the most important feature of the backpack invented by Lawrence C. Rome and his colleagues?
A.
It produces electricity for electronic devisees while the wearer walks.
B.
It can be used as cell phones, GPS in the military actions or field studies.
C.
It is small and convenient.
D.
It is light and easy to carry.