The spring is compressed by a distance a and released. The block again comes to rest when the spring is elongated by a distance `b`. During this
A. Work done by the spring on the block `=1/2k(a+b)^(2)`
B. Work done by the spring on the block `=1/2 k(a^(2)-b^(2))`
C. Coefficient of friction `=(k(a-b))/(2mg)`
D. Coefficient of friction `=(k(a+b))/(2mg)`
