指示功反映了发动机气缸在一个工作循环中所获得的（）的数量。
A.有用功
B.无用功
C.机械总功
D.热能
参考答案：A
The workers _____busily when the boss came to look for something she ______in the office.
A had worked, had left B were working ; had left C working ; had left D had worked; left
甲状腺的主要供血动脉有几根（）
A.2根
B.3根
C.4根
D.5根
E.6根
