What is the reason for this behavior?

Refer to the exhibit.

R1(config)#ip sla 1

R1(config-ip-sla)#icmp-echo 172.20.20.2 source-interface FastEthernet1/0 R1(config-ip-sla-echo)#timeout 5000 R1(config-ip-sla-echo)#frequency 10

R1(config-ip-sla-echo)#threshold 500

R1(config)#ip sla schedule 1 start-time now life forever

R1(config)#track 10 ip sla 1 reachability

R1(config)#ip route 0.0.0.0 0.0.0.0 172.20.20.2

After implementing the configuration 172.20.20.2 stops replaying to ICMP echoes, but the default route fails to be removed.

What is the reason for this behavior?
A . The source-interface is configured incorrectly.
B . The destination must be 172.30.30.2 for icmp-echo
C . The default route is missing the track feature
D . The threshold value is wrong