Refer to the exhibit. Which address range efficiently summarizes the routing table of the addresses for router Main?

The 172.16.0.0./20 network is the best option as it includes all networks from 172.16.0.0 – 172.16.16.0 and does it more efficiently than the /16 and /18 subnets.
The /21 subnet will not include all the other subnets in this one single summarized address.