An elastic spring of unstretched length `L` and force constant `K` is stretched by amoun t `x` .It is further stretched by another length `y` The work done in the second streaching is
A. `(1)/(2)kbeta^2`
B. `(1)/(2)k(alpha^2+beta^2)`
C. `(1)/(2)k(alpha+beta)^2`
D. `(1)/(2)kbeta(2alpha+beta)`