系统备用容量中，按其状态分时，当发电机组在开机状态下的备用称为（）备用.
A、旋转；
B、检修；
C、国民经济；
D、事故。
参考答案：A
Mr Li ____ England. He ____ London for two weeks.
A．has been to; has been to
B．has gone to; has been in
C．has been to; has been in
D．has gone to; has been to
爬山和上楼属于承重运动，跳绳属于非承重运动。
