Which connection uses the default encapsulation for serial interfaces on Cisco routers?

A.
The serial connection to the NorthCoast branch office.

B.
The serial connection to the North branch office.

C.
The serial connection to the Southlands branch office.

D.
The serial connection to the Multinational Core.

Explanation:
Cisco default encapsulation is HDLC which is by default enabled on all cisco router.
If we want to enable other encapsulation protocol(PPP,X.25 etc) we need to define in interface
setting. But here except s1/1 all interface defined by other encapsulation protocol so we will
assume default encapsulation running on s1/1 interface and s1/1 interface connected with North