[单选题]
The grand unified theorn h c5f5t:vr:py ( mn7xv4u7iba ;u2gxu xu+3h a1GUT) is a sought-after model that would unify three of the four forces of nature. Whichuhaua ; +u1xg 3uxmx247ni7vb force is the one it would not include?
A. gravitational
B. strong
C. weak
D. electromagnetic
