You suspect that a gateway machine on your network has failed but you are unsure which machine.
Which command will help locate the problem?

A.
traceroute

B.
nslookup

C.
ps

D.
ifconfig

E.
netstat

Explanation:
nslookup deals with domain name servers, not gateway / routing servers
ps displays process information
ifconfig displays/configures network interfaces, not routing information between servers
netstat prints network configuration, routing tables, interface statistic, masquerade connections, and multicast memberships

traceroute is the best answer because it tracks and prints routing packets across a network on their way to a given host.