由于电压脱落或频率超出规定范围而退出电网的风电机组（）在电压和频率恢复后自行并入电网。

A.可以

B.不可以

C.不确定是否可以

D.其他三个选项都不是

Ms Black is considered a________lady by her neighbors, for she often helps the poor old man next door.  [      ]

A. generous  

B. hopeful

C. mean  

D. selfish