Since , "F = ma".. which also gives "a = F/m".....Here we got a relation that "a" is inversely proportional to "m"...... So we can conclude that if "a" increases, then "m" decreases & if "a" decreases, then "m" increases............ So,the answr is C, thats all.

Introduction:
In order to understand why the acceleration of a body may sometimes increase and sometimes decrease when its mass increases, we need to consider Newton's second law of motion. This law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. Mathematically, it can be expressed as follows:

F = ma

Where:
F = net force acting on the body
m = mass of the body
a = acceleration of the body

Explanation:
When the mass of a body increases while the net force acting on it remains constant, the acceleration of the body can change in different scenarios:

1. Decreased Acceleration:
If the mass of the body increases, while the net force remains constant, the acceleration will decrease. This can be understood by rearranging Newton's second law equation:

a = F/m

As the mass (m) increases, the denominator in the equation becomes larger, resulting in a smaller acceleration (a). Therefore, the acceleration of the body decreases when its mass increases.

2. Remains the Same:
In some cases, the increase in mass may be compensated by an increase in the net force acting on the body. If the force is increased in proportion to the increase in mass, the acceleration can remain the same. This occurs when the net force is adjusted to counterbalance the effect of increased mass, resulting in the same acceleration as before.

3. Sometimes Increases:
In certain situations, the increase in mass may lead to an increase in acceleration. This happens when the net force acting on the body increases more than the increase in mass. In other words, if the force is increased at a higher rate than the mass, the acceleration will increase.

Conclusion:
In summary, when the mass of a body increases while the net force acting on it remains constant, the acceleration of the body can either decrease, remain the same, or increase. The specific outcome depends on the relationship between the increase in mass and the net force. It is important to consider both factors to determine how the acceleration will be affected.