Let a1, a2, a3, a4 be real numbers such that a1+a2+a3+a4 = 0 and a12+a22+a32+a42 = 1. Then, the smallest possible value of the expression (a1-a2)2 + (a2-a3)2 + (a3-a4) + (a4-a1)2 lies in the interval
(a) (0, 1.5)
(b) (1.5, 2.5)
(c) (2.5, 3)
(d) (3, 3.5)