Final answer:
Mass and weight are directly proportional to each other; as the mass of an object increases, so does its weight when in a constant gravitational field.
Step-by-step explanation:
While mass and weight are not the same, they are directly proportional to each other. The weight of an object is the gravitational force exerted on it, which is directly proportional to the mass of the object (as long as the gravitational field is constant). For example, on Earth, an object's weight is calculated as the product of its mass and the gravitational acceleration (about 9.81 m/s2). Thus, if the mass of an object doubles, its weight also doubles, indicating a direct proportionality. In contrast, inversely proportional means that an increase in one variable results in a corresponding decrease in the other, which is not the case here. Therefore, the correct answer to the student's question is a) Directly proportional.