The average cost when producing x items is found by dividing the cost function, C(x), by the number of items, x. When is the average cost less than 100, given the cost function is C(x) = 10x + 360?

A.) (0,4)
B.) (-infinity, 0) U (4, infinity)
C.) (4, infinity)
D.) (-infinity, 0] U [4, infinity)