发电机是利用______现象制成的．通过发电机把______转化为电能；通电线圈在磁场里发生转动，实现了电能转化为______能；电磁继电器是利用______控制工作电路通断的开关．

—The police have caught the murderer.

　　   —Yes, and he admitted ________ his boss on a rainy night seven years ago.

A．to kill

B．to have killed

C．having killed

D．have been killing