What is the effect of the ASA command crypto isakmp nat-traversal?

What is the effect of the ASA command crypto isakmp nat-traversal?
A . It opens port 4500 only on the outside interface.
B . It opens port 500 only on the inside interface.
C . It opens port 500 only on the outside interface.
D . It opens port 4500 on all interfaces that are IPSec enabled.

Answer: D