The relationship between force and position is shown in figure given (in one dimensional case). The work done by the force is displaying a body from $x=1 \mathrm{~cm}$ to $x=5 \mathrm{~cm}$ is
(a) $20 \mathrm{erg}$
(b) $60 \mathrm{erg}$
(c) 70 erg
(d) $700 \mathrm{erg}$