[单选题]
A force moves an objemdvho)gf :4 0ry( jw i81)3j, biq yk+idwkn.dct in the direction of the force. The graph in Fig. 6-1 shows the force versus the object's position. Find the work done when the object moves from 4.0 tk8( iyjnwy1bd,qijk3. iwd+) o 6.0 m.
A. $20 \; J$
B. $40 \; J$
C. $60 \; J$
D. $80 \; J$