Right choice is (c) PL/EAg
The best explanation: The displacement, that is increase in length of tension member, under service load is given by Δ = PL/EAg, where Δ = Elongation of member in mm, P= unfactored axial load in N, L = length of member in mm, E = elastic modulus = 2×10^5MPa, Ag = gross cross sectional area of member in mm^2.