________the help of the teacher, the student who wasn't good at math________the difficult problem

quickly.[ ]

A. Under; worked out  

B. With; worked on

C. Under solved  

D. With; solved

起重机进行维修和保养是起重机使用和管理的重要内容，是（）的职责。

A.专职维修人员；

B.起重机司机、安全技术人员；

C.起重机司机、专职维修人员；

D.安全技术人员、起重机司机、专职维修人员。