There's old tree in front of house. [ ]
A. a; an
B. an; the
C. a; the
D. my; her
答案:B
轴承首次装用年月应刻打在滚动轴承标志板的()。
A.A栏
B.C栏
C.左A栏
D.右B栏
凝汽器的真空是如何形成、建立和维持的?