Part D

Why are the two$-$source interference equations not valid for light from an incandescent bulb that passes through a screen with two narrow slits onto an observation screen directly behind it$?$

not monochromatic sources

incoherent sources

observed from a distance similar to or smaller than the separation between the sources

$1$ only $2$ only $3$ only $1$ and $2$ only $1$ and $3$ only $2$ and $3$ only $$all three