Which type of voice port will be most cost effective to allow the gateway to terminate two circuits from the PSTN or a PBX?

Which type of voice port will be most cost effective to allow the gateway to terminate two circuits
from the PSTN or a PBX?

A.
FXO

B.
FXS

C.
PRI T1

D.
E1

E.
E&M

F.
BRI

G.
CAS T1

H.
E1