1). B [a>0]
2). D [none of the above]
Acceleration depends on the direction and magnitude of
1). As velocity is increasing that means change in velocity with
time is positive. This implies a>0.
2). In other case, we know that speed is only the magnitude of
the velocity. If speed increases that means an object can first go
straight and then backwards or in any direction ( only the distance
matters not the displacement from initial position) so we can't say
actually whether the acceleration is positive or negative.
If the acceleration is negative it can increase the speed in
opposite direction with time and if it's positive then it can
increase the velocity as well as speed with time.
And a zero acceleration represents a constant velocity.
So for speed to be increasing acceleration can be positive as
well as negative also.
B and C both can be written with answer.
Or you can say D is answer if only one is correct.