The graph between the displacement `x` and time `t` for a particle moving in a straight line is shown in the figure. During the interval `OA, AB, BC` and `CD` the acceleration of the particle is
`OA, AB, BC, CD`
A. `OA=+, AB=0, BC=+, CD=+`
B. `OA=-, AB=0, BC=+, CD=0`
C. `OA=+, AB=0, BC=-, CD=+`
D. `OA=-, AB=0, BC=0, CD=+`