[单选题]
The grand unified theory (GUT) is a sought-afterv+;p(to/ zyvu mo/x5bw26 cp iyo*mgt gc9pmn/ 94 ob7gzdel that would unify three of the four forces of nature. Which force im95pc bm6/ o oi7 g/xny2gw 9gbtzp*4cs the one it would not include?
A. gravitational
B. strong
C. weak
D. electromagnetic
