[单选题]
A force moves an object in the4rds1;bzdf n7 k1r1sl direction of the force. Th cq c7e 6m-ok8oetb58ve graph in Fig. 6-1 shows the f7-m 8o qcveo6cteb 8k5orce versus the object's position. Find the work done when the object moves from 2.0 to 4.0 m.
A. $20 \; J$
B. $40 \; J$
C. $60 \; J$
D. $80 \; J$