Which of the following is the correct formula for encoding PCM?

A.
2 states per bit x 8000 Hz frequency coded into 4 bits = 64 kbps

B.
8000 Hz frequency encoded in 4 bits, each expanded by two = 64 kbps

C.
3400 Hz voice frequency represented in 8 bits x 2 states per bit = 56bkps

D.
4000 Hz frequency sampled at two times the frequency and each sample is represented in 8 bits = 64 kbps