According to Newton's second law of motion, \( F = ma \), where \( F \) is the net force, \( m \) is the mass, and \( a \) is the acceleration. If the net force \( F \) remains a nonzero constant and the mass \( m \) increases, the acceleration \( a \) can be found using the equation:
\[ a = \frac{F}{m} \]
As the mass \( m \) increases while \( F \) stays constant, the acceleration \( a \) must decrease. This is because the same force is being divided by a larger mass.
Therefore, the correct response is:
The acceleration decreases.