Find the greatest common factor of the expressions below, if one exists. $40(7-y{)}^5,50(7-y{)}^4$

A) $40(7-y{)}^4$
B) $5(7-y{)}^{10}$
C) $10(7-y{)}^4$
D) $4(7-y{)}^5$
E) No greatest common monomial factor exists.