b.his reflection seems to be a part of the war memorial wall.
In the poem, the speaker is visiting the Vietnam Veteran's Memorial and sees his reflection in the granite. This immediately eliminates option A and D. In the lines, he says, "I'm stone" and "my clouded reflection eyes me". Both of these lines indicate that the speaker feels as though he is inside of the memorial. We don't know from these lines if he feels trapped in the war.