30. The following graphs relate to two objects that start at $x = 0$ at $t = 0$ and move in one dimension independently of one another. Graphs, of the velocity of each object versus time are shown below
Object A
$v$ (m/sec)
1.0
10
20
$t$ (sec)
-1.0
Object B
$v$ (m/sec)
1.0
10
20
$t$ (sec)
-1.0
Which object moves with constant non-zero acceleration?
(A) A
(B) B
(C) both A and B
(D) neither A nor B