A wire of length L, area of cross section A is hanging from a fixed support. The length of the wire changes to `` L_1 `` when mass M is suspended from its free end. The expression for Young’s modulus is:
(A) `` \frac {MgL_1}{AL} ``
(B) `` \frac {Mg(L_1-L)}{AL} ``
(C) `` \frac {MgL}{AL_1} ``
(D) `` \frac {MgL}{A(L_1-L)} ``