Which call would most likely require an audio transcoder?

Which call would most likely require an audio transcoder?

A.
128-kbps ISDN call to MCU

B.
128-kbps H.323 call to MCU

C.
128-kbps ISDN call to H.323 endpoint

D.
384-kbps ISDN call to H.323 endpoint

E.
384-kbps H.323 call to MCU