机件上的肋板当剖切平面通过肋板厚度的对称平面或轮辐的轴线时,这些结构()剖面符号。
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The treatment will continue until the patient reaches the point ________ he can walk correctly and safely.
A. when
B. where
C. which
D. whose
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A. which
B. where
C. when
D. what
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B. 操作系统
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