If the mass of an object increases, how is its acceleration affected, assuming the net force acting on the object remains the same?

Based on Newton's second law of motion, the net force applied to an object is equal to the product of the mass of the object and the acceleration it experiences. That is,
  
          F = ma

If we are to assume that the net force is constant and that the mass is increased, the acceleration should therefore decrease in order to make constant the value at the right-hand side of the equation. 

The answer is a.  i hope this