A wire elongates by $l \mathrm{~mm}$ when a load $w$ is hanged from it. If the wire goes over a pulley and two weights $w$ each are hung at the two ends, then the elongation of the wire will be (in $\mathrm{mm}$ ) [2006]
(A) $l$
(B) $2 l$
(C) Zero
(D) $1 / 2$