—You will be late _____ you hurry up.     

—Don't worry. I still have enough time.       [ ]

A. if

B. until

C. unless

D. because

变压器的铁芯是采用相互绝缘的薄硅钢片叠成，从而达到（）目的。

A.增大涡流

B.减小电阻率

C.减小涡流

D.减小阻抗