Which of the following could result from a substance that undergoes a physical change?
a) its chemical composition is altered.
b) it has an irreversible change.
c) it forms a new substance.
d) its shape is altered.

Its shape is altered.

Explanation:

For example, an ice cube melting into a puddle.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.