Listen! Someone ________ an English song now.[ ]

A. sings            

B. sang          

C. is singing    

D. was singing

风力发电机组中，测量温度用PT100在室温下阻值正常为（）

A.90—100欧姆

B.100—120欧姆

C.120—140欧姆

D.正的无穷大