What can be done to address this problem?

Refer to the exhibit.

Router4 can ping Router5 (172.16.6.5), but not Router7 (172.16.11.7). There are no routing protocols running in any of the routers, and Router4 has Router6 as its default gateway. What can be done to address this problem?

Exhibit:

A.
Convert to static NAT.

B.
Convert to dynamic NAT.

C.
Add a static route in Router7 back to Router4.

D.
Change the inside and outside NAT commands.