气门弹簧座一般是通过（）或（）固定在气门杆尾端的。
参考答案：锁块；锁销
The foreign teacher __________ in our school for ten years and does not want to leave.[ ]
A. worked
B. works
C. is working
D. has worked
食堂生产场所周围（）米内无有毒有害场所。
A.20
B.30
C.40
D.50
