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【单选题】
图示为一方桌的对称平面，水平拉力【图片】和桌子重【图片】都作用在对称平面内，桌腿【图片】、【图片】与地面之间的静滑动摩擦系数为f。若在对称平面内研究桌子所受的滑动摩擦力。以下四种情况下哪一种说法是正确的？【图片】A.
当 时，滑动摩擦力为
B.
当 时，滑动摩擦力为
C.
当 时，滑动摩擦力为
D.
当 时，滑动摩擦力为
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参考解析：
知识点：
皮皮学刷刷变学霸
举一反三
【单选题】Why passengers in a cruise ship sitting in the port of Yokohama were not allowed to leave the ship 14 days ago?
A.
Because all of the passengers in this ship had been infected by new coronavirus.
B.
Because some passenger in this cruise ship were found to have been infected by new coronavirus.
C.
Because they had to be under quarantine.
D.
Because they didn’t want to leave.
【单选题】将健康人的组织或器官来替代患者丧失功能的组织和器官,常 常会发生排斥反应,此时HLA分子被认为是
A.
同种异型抗原
B.
异嗜性抗原
C.
同种抗原
D.
异种抗原
E.
改变的自身抗原
【单选题】According to paragraph 1, why is it difficult to determine when the first clipper ship was built?
A.
The clipper predates written records by almost 75 years.
B.
Sailors kept the details of their vessels tightly guarded secrets.
C.
The clipper has no technical specifications that can be used to identify it.
D.
The term 'clipper' was originally used to describe a variety of ships.
【单选题】将健康人的组织或器官来替代患者丧失功能的组织和器官,常常会发生排斥反应,此时 HLA 分子被认为是:
A.
异种抗原
B.
同种异型抗原
C.
自身抗原
D.
异嗜性抗原
E.
改变的自身抗原
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