一台三相异步电动机的磁极对数p=2,电源频率为50Hz,电动机转速n=1440r/min,其转差率s为()
选项：

A:0.01000000000000000020816681711721685132943093776702880859375
B:0.0200000000000000004163336342344337026588618755340576171875
C:0.0299999999999999988897769753748434595763683319091796875
D:0.040000000000000000832667268468867405317723751068115234375