What is the size of a point-to-point GRE header, and Protocol number at IP layer?

A.
8 byte, and 74

B.
4 byte, and 47

C.
2 byte, and 71

D.
24 byte, and 1

Explanation:
Explaination
Protocol suite: TCP/IP. Type: Transport layer encapsulation protocol. IP Protocol: 47.
Generic Routing Encapsulation (GRE)
Packet header The GRE packet header has the form:

Flags and version (2 octets)
The GRE flags are encoded in the first two octets. Bit 0 is the most significant bit, bit 15 is the least significant bit. Bits 13 through 15 are reserved for the Version field. Bits 5 through 12 are reserved for future use and MUST be transmitted as zero.

RFC 1701 Generic Routing Encapsulation (GRE) October 1994 Checksum Present (bit 0)
If the Checksum Present bit is set to 1, then the Checksum field is present and contains valid information. If either the Checksum Present bit or the Routing Present bit are set, BOTH the Checksum and Offset fields are present in the GRE packet. Routing Present (bit 1) If the Routing Present bit is set to 1, then it indicates that the Offset and Routing fields are present and contain valid information. If either the Checksum Present bit or the Routing Present bit are set, BOTH the Checksum and Offset fields are present in the GRE packet.

Key Present (bit 2) If the Key Present bit is set to 1, then it indicates that the Key field is present in the GRE header. Otherwise, the Key field is not present in the GRE header. Sequence Number Present (bit 3) If the Sequence Number Present bit is set to 1, then it indicates that the Sequence Number field is present. Otherwise, the Sequence Number field is not present in the GRE header.
Strict Source Route (bit 4) The meaning of the Strict Source route bit is defined in other documents. It is recommended that this bit only be set to 1 if all of the the Routing Information consists of Strict Source Routes.
Recursion Control (bits 5-7) Recursion control contains a three bit unsigned integer which contains the number of additional encapsulations which are permissible. This SHOULD default to zero.
RFC 1701 & 2890