[单选题]
A force moves an object ii 3o z,wpvd8s(n the diuytb th7uvd wjr.(9;, rection of the force. The graph in Fig. 6-1 shr;b7h9u t yjtuv.w(,dows the force versus the object's position. Find the work done when the object moves from 4.0 to 6.0 m.
A. $20 \; J$
B. $40 \; J$
C. $60 \; J$
D. $80 \; J$
