Which tool, command or service allows a remote or local user to find any open connection paths to the system on the Internet or an intranet?

A.
Traceroute

B.
Whois

C.
Nslookup

D.
Port scanner

Explanation:
A port scanner is used to identify active ports which are open.
Incorrect Answers:
A: Traceroute is used to identify the hops to a target host, and is used for mapping the structure of the network.
B: Whois is used to get primary and secondary DNS server information.
C: NSLOOKUP is used to query a DNS server.