I chose A because of the last paragraph stating that the two styles --periodically between banded and bordered-- suggested altered visual and motor habited occurred. Since this is before the supposed Anglo influence, I thought it could be assumed that Navajo motor habits and though processes might have caused the style change from banded possibly. And so the author might agree with the statement.
The last paragraph also made me turn away from D since the idea of motor habits changing seemed to trump the 4th paragraph idea that no radical revisions and thus change to motor habits need be assumed. The example in the last paragraph signaled to me more as a pointer to the time period of motor habit changes rather than the idea that it the transition to isolated figures was gradual.