Which two devices can be used to complete the connection between the WAN router at the customer site and the service provider?

Refer to the exhibit. Which two devices can be used to complete the connection between the WAN router at the customer site and the service provider?

A.
modem

B.
Frame Relay switch

C.
CSU/DSU

D.
WAN switch

E.
ISDN TA

F.
ATM switch