An arithmetic gradient series ?explain please A) starts at zero at the end of the first period and then increases by a constant amount each period. B) starts at zero at the beginning of the first period and then increases by a constant amount each period. C) starts at zero at the end of the second period and then increases by a constant amount each period. D) starts at zero at the beginning of the second period and then increases by a constant amount each period. E) starts at zero at the end of the first period and then increases by an increasing amount each period