what is the BER (bit error rate) if there is 1 bit error every four days?

For an OC-48 signal (2.5Gb/s), what is the BER (bit error rate) if there is 1 bit error every four days?

A.
10E-12

B.
10E-13

C.
10E-14

D.
10E-15

E.
10E-16