Factor Out the Greatest Common Monomial Factor from the Polynomial $21 y - 12$

Multiple Choice

Factor out the greatest common monomial factor from the polynomial $21 y - 12$ .

A) $12 ( 21 y - 4 )$
B) $21 ( y - 4 )$
C) $3 ( 7 y - 12 )$
D) $3 ( 7 y - 4 )$
E) no common factor other than 1