4. Given in rectangle $A B C D$, $A B=72, A D=$ 56. If $A B$ is divided into 72 equal parts, and parallel lines to $A D$ are drawn through each division point; and if $A D$ is divided into 56 equal parts, and parallel lines to $A B$ are drawn through each division point, then these parallel lines divide the entire rectangle into $72 \times 56$ small squares with side length 1. Thus, the number of small squares that are internally crossed by the diagonal $A C$ (the interior of the small square contains at least two points on $A C$) is ( ) .
(A) 130
(B) 129
(C) 121
(D) 120