[单选题]
The grand unified theory (GUT) is a so ;qa;u-ftrm7fv4f d:yught-after model t yu g,9t myc4y0w5iw-ohat would unify three of the four forces of naturioyy 594 gymcwtw- ,u0e. Which force is the one it would not include?
A. gravitational
B. strong
C. weak
D. electromagnetic