AWS Certified Solutions Architect Associate Test 3

You can create an alias resource record set at the zone apex. You cannot create a CNAME record at the top node of a DNS namespace, also known as the zone apex. For example, if you register the DNS name example.com, the zone apex is example.com.
http://docs.aws.amazon.com/Route53/latest/DeveloperGuide/resource-record-sets-choosing-alias- non-alias.html