50. When a certain rubber band is stretched a distance x, it exerts a restoring force F = ax + bx2 , where a and b are constants. The work done in stretching this rubber band from x = 0 to x = L is:
(A) aL2 + bLx3
(B) aL + 2bL2
(C) a + 2bL
(D) bL
(E) aL2 /2 + bL3 /3
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