Answer:
D) Acceleration is positive and increasing.
Step-by-step explanation:
Acceleration is defined as the rate of change of velocity per unit time; in formulas:

where
is the variation of velocity and
is the variation in time.
The graph shows the velocity vs the time of a moving object. We can see that
is the increment on the y-axis, while
is the increment on the x axis: therefore, the ratio
is the slope of the curve. In fact, in a velocity-time graph, the slope of the curve corresponds to the acceleration of the object.
In this particular graph, we see that the slope of the curve continues to increase: therefore, the acceleration is positive (because the slope is positive, since the velocity is increasing) and increasing (because the slope is increasing).