特种作业人员上岗前必须接受专门的培训，经考试合格取得()证书，方可上岗作业。
A.大学专科学历
B.执业资格
C.职业技能
D.操作资格
参考答案：D
Zhuhou, _______ on the Xiang River, is an important city, second only to Changsha.
A．located
B．locating
C．being located
D．to be located
压力开关的工作原理是什么？
