Displacement-time curve of a particle moving along a straight line is shown. Tangents at A and B make angles 45° and 135° with positive x-axis respectively. The average acceleration of the particle during t = 1 to t = 2 second is :
(A) – 2 m/s2
(B) 1 m/s2
(C) – 1 m/s2
(D) zero