指南针发明于[ ]
A.战国
B.汉朝
C.北宋
D.南宋
答案:C
It is ______ for me to follow the Australian guests because I am good at English.
A.bad
B.easy
C.hard
D.right
电费核算是电费管理的什么环节,是为提高供电企业经济效益服务的?