Which routers must be Level 2 routers?

Refer to the exhibit.

All routers are running IS-IS. Which routers must be Level 2 routers?

A.
B, D, E and G

B.
A, D, E, and H

C.
B, C, F, and G

D.
B, C, E, F, and G

E.
A, B, C, D, F, G, and H