矿井提升机主轴轴承通常采用（）润滑。
A、油绳
B、强制给油
C、油环
D、油池润滑
参考答案：B
The speaker, Professor Davie, __________ for his impressive achievements in physics, was warmly received by all the students in our school.
A．being known
B．known
C．having known
D．to know
被喻为细胞内的“动力工厂”的结构是
A．叶绿体
B．细胞膜
C．线粒体
D．细胞核
