正解:A
In DNS, the PTR (Pointer) record is used specifically in reverse DNS lookups to map an IP address to a domain name, which is the opposite of the more common forward DNS lookups that map domain names to IP addresses. The PTR record is the principal type of record used in reverse DNS lookups, making it the correct answer. AAAA records store IPv6 addresses, CNAME records are used for aliases, and TXT records hold text information, none of which are primarily used in reverse DNS configurations.