[单选题]
The grand unified theory (GU,2/ )dz .am9b6owtn pq8bb pqsT) i9tr / t)3l4zan.uyb7nwgf d9 ms a sought-after model that would unify three of the four forces of nature. Which force is the one it would no/9n4wf 7 btgu.dnm ta)3lr9zyt include?
A. gravitational
B. strong
C. weak
D. electromagnetic
