In a lab, R1 connects to R2, which connects to R3. R1 and R2 each have several working interfaces, all assigned addresses in class A network 10.0.0.0. Router R3 has some working interfaces in class A net work 10.0.0.0, and others in class B network 172.16.0.0. The engineer experiments with the auto -summary command on R2 and R3, enabling and disabling the command in various combinations. Which of the following combinations will result in R1 seeing a rout e for 172.16.0.0/16, instead of the individual subnets of class B network 172.16.0.0?（）

A. auto - summary on R2 and no auto - summary on R3
B. auto - summary on R2 and auto - summary on R3
C. no auto -summary on R2 and no auto- summary on R3
D. no auto - summary on R2 and auto - summary on R3