a. Based on the comment, the concentrator subnet is 172.16.1.0/24. Clients should get an IP from this subnet, it's included in AutoVPN, so they should be able to talk to each other. So this is a possible answer.
b. Mandatory DHCP is disabled, so static IP addresses are allowed. This answer can not be correct.
c. Based on the comment that the concentrator VLAN is 172.16.1.0/8 this answer can not be correct.
d. 22.214.171.124 is not in the AutoVPN include list, so it can't be correct.