I'm having trouble with interference?

[SAump]

PLAY: Batter hits ball to shortstop, who fields ball but throws wild past first baseman. The offensive coach at first base, to avoid being hit by the ball, falls to the ground and the first baseman on his way to retrieve the wild thrown ball, runs into the coach; the batter-runner finally ends up on third base. The question is asked whether the umpire should call interference on the part of the coach. This would be up to the judgment of the umpire and if the umpire felt that the coach did all he could to avoid interfering with the play, no interference need be called. If it appeared to the umpire that the coach was obviously just making it appear he was trying not to interfere, the umpire should rule interference.

Umpire ruled this "intentional interference, regardless of what his thought may have been." Place the runner.
A) 1B
B) 2B
C) 3B
d) Out