Amy ____ the school library. She ______ books three times a week.

A．has gone to; has used to borrow

B．has been to; used to borrow

C．has gone to; has been used to borrowing

D．has been to; is used to borrowing

相控整流电路的输入端功率因数PF（）。

A、跟位移因数有关

B、跟波形畸变因数有关

C、跟位移因数和波形畸变因数均无关

D、跟位移因数与波形畸变因数的乘积有关