Explanation/Reference:
Explanation
EIGRP performs an auto-summarization each time it crosses a border between two different major networks. In this case all different networks are in different major networks so EIGRP will perform auto- summarization when it exits an interface. But R1 has been configured with no auto-summary command so EIGRP will not summarize on S0 interface of R1. So the routing table of R2 will have the network
10.10.10.0/24 (not be summarized).
When exiting S1 interface of R2, EIGRP summarizes network 172.16.10.0/24 into the major 172.16.0.0/16 network but it does not summarize network 10.10.10.0/24 because it is not directly connected with this network. Therefore in the routing table of R3 there will have:
+ Network 10.10.10.0/24 ( not summarized)
+ Network 172.16.0.0/16 (summarized)
-> C and D are correct.
Note: I simulated this question on GNS3, you can see the final outputs of the show ip route commands on these routers (I connected these routers via FastEthernet, not Serial interfaces so the outputs are slightly different but the main points are not changed).