According to Newton's second law of motion, the relationship between force, mass, and acceleration is given by the equation:
\[ F = ma \]
Where:
- \( F \) is the net force,
- \( m \) is the mass,
- \( a \) is the acceleration.
If the net force \( F \) is a non-zero constant and the mass \( m \) increases, we can rearrange the equation to solve for acceleration:
\[ a = \frac{F}{m} \]
Since \( F \) is constant and \( m \) is increasing, the acceleration \( a \) must decrease.
Therefore, the correct response is:
The acceleration decreases.