The correct option is D (a) and (c) are correct.
It is given that a=f(v)
⇒vdvdx=f(v)
⇒x∫0dx=∫vdvf(v)
⇒x=∫vdvf(v)
If acceleration is a linear function of velocity, the a−v graph will be a straight line, e.g., if a=4v+5 and a−v graph will be straight line. Hence, in this case slope of a−v graph will be constant.
As acceleration is dependent on velocity and acceleration will change v, so acceleration will also change and can’t remain constant.
So, the correct answer is option (d).