Correct Answer  Option 2 : uniform acceleration
CONCEPT:

Velocity: The rate of change of displacement is called velocity.
 The slope of the positiontime graph or displacement  time graph gives the velocity.
Velocity (v) = dx/dt
Where x is displacement and t is time

Acceleration: The rate of change in velocity is called acceleration.
 The slope of a velocitytime graph gives the acceleration.
Acceleration (a) = dv/dt
 Anything (that is velocity, acceleration, or speed) which is constant is called uniform (uniform velocity, uniform acceleration, or uniform speed).
EXPLANATION:
Given that:
v ∝ t
v = kt
where k is a constant.
Acceleration (a) = dv/dt = k = constant
Hence the object has uniform acceleration.