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

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

• The serial connection to the MidEast branch office.
• The serial connection to the DeepSouth branch office.
• The serial connection to the NorthCentral branch office.
• The serial connection to the Multinational Core.

Explanation: On the basis of the configuration on Dubai provided in the exhibit, we know that the encapsulation types of different interfaces are as follows:
Serial 1/0 : encapsulation frame-relay
Serial 1/2 and Serial 1/3 : both interfaces are encapsulated PPP
Serial 1/1: There is no related encapsulation information displayed, so its default encapsulation type is HDLC .
Based on the network topology provided in the exhibit, the interface Serial 1/1 is connected to the router
MidEast of the branch office, so the encapsulation type of the router MidEast is by default.
The default encapsulation on a serial interface is HDLC. The original HDLC encapsulation was defined by the International Organization for Standards (ISO), those same folks who developed the OSI model. The ISO version of HDLC had one shortcoming, however; it had no options to support multiple
Layer 3 routed protocols. As a result, most vendors have created their own form of HDLC. Cisco is no exception because it has its own proprietary form of HDLC to support various Layer 3 protocols such as IPX, IP, and AppleTalk.
The Serial connection to the Dub branch office using the default encapsulation type. You can change using:
* encapsulation command on interface

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