Refer to the exhibit.

R1 needs a route to the remote LAN 20.20.20.0/24 behind R3. The correct static route uses the next-hop address on the adjacent router, 10.10.10.2. That is why option D is correct. A default gateway command is not the correct fix on a router that is already routing; routers use routes in the routing table, not an end-host default gateway setting, to forward packets. Setting a default network is also not the precise repair because the problem is reachability to one known remote subnet. Using only the exit interface on an Ethernet network is weaker design because the router may need ARP resolution for each destination and can create ambiguity on multiaccess media. A next-hop static route states exactly where R1 must send packets for 20.20.20.0/24. This matches the CCNA 200-301 v1.1 IP Connectivity requirement to configure and verify IPv4 static routes. Reference: Cisco IOS static routing behavior and CCNA 200-301 v1.1 routing objectives.