What is the most efficient summarization that R1 can use to advertise its networks to R2?

Refer to the exhibit.

What is the most efficient summarization that R1 can use to advertise its networks to R2?
A. 172.1.0.0/24
B. 172.1.2.0/21
C. 172.1.4.0/22
D.

E.

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