Let f(x) = ax^2 + bx + c, where a, b, c are integers. Suppose f(1) = 0, 40 < f(6) < 50, 60 < f(7) < 70, and
1000t < f(50) < 1000 (t + 1) for some integer t. Then the value of t is
(A) 2 (B) 3 (C) 4 (D) 5 or more