A router has four interfaces addressed as 10.1.1.1/24, 10.1.2.1/24, 10.1.3.1/24, and 10.1.4.1/24. What is the smallest summary route that can be advertised covering these four subnets? 

Answer options:

A. 10.1.2.0/22
B. 10.1.0.0/22
C. 10.1.0.0/21
D. 10.1.0.0/16

C