First Baseman Holding Runner in Foul Territory

 
With a runner (R1) on first base, the first baseman is holding the runner on base, but standing with both feet in foul territory. The pitcher is about to get on the rubber to take his signs from the catcher. What do the umpires do?

A) The first baseman is in a legal position, there is no action needed.
B) The first baseman is not in a legal position, so this is a balk and award R1 second base
C) The umpire should not put the ball in play until the first baseman has both feet in fair territory
D) The umpire should not put the ball in play until the first baseman has one foot in fair territory
 
Call
In NF, at the time of the pitch, all fielders need to be in fair territory -- which is defined as having at least one foot in fair territory (NF 1-1-4 and casebook 1.1.4).
 
In the situation below, "D": The umpire should not put the ball in play until the first baseman has one foot in fair territory.