What is the most efficient summarization that R1 can use to advertise its networks to R2()。
- A172.1.0.0/22
- B172.1.0.0/21
- C172.1.4.0/22
- D172.1.4.0/24 172.1.5.0/24 172.1.6.0/24 172.1.7.0/24
- E172.1.4.0/25 172.1.4.128/25 172.1.5.0/24 172.1.6.0/24 172.1.7.0/24