Question

a mass accelerates uniformly when the resultant force on it:
1. increases uniformly with respect to time
2. is constant but not zero
3. is proportional to the displacement from a fixed point
4. i proportional to velocity

Answer 1

F = ma
So if you want the "a" to stay constant (as it is then uniform acceleration), the F must also be constant to apply a constant force.

2 is the answer