闭式蜗杆传动的主要失效形式是()。
A、蜗杆断裂
B、蜗轮轮齿折断
C、胶合、疲劳点蚀
D、磨粒磨损
参考答案:C
—Where's your father?
—He ______ to work.[ ]
A. has gone
B. went
C. has been
D. will go
人类B细胞分化、成熟的场所是
A.胸腺B.骨髓C.法氏囊D.脾脏E.淋巴结