A body of mass ‘m’ is attached to the lower end of a metal wire, whose upper end is fixed. If the elongation in the wire is ‘l ’, the correct choices of the following are 
a) Loss in potential energy of mass is mgl
b) Elastic potential energy stored in the wire is  $\frac{mg\mathcal{l}}{2}$
c) Elastic potential energy stored in the wire is mgl
d) Heat produced is $\frac{mg\mathcal{l}}{2}$

• A

  a, c only

• B

  a,b,d

• C

  c,d only

• D

  a,c,d