C - chemical change
P- physical change

(Pls help me)

Burning wood is a chemical change.  Burning wood is an example of a chemical reaction in which wood in the presence of heat and oxygen is transformed into carbon dioxide, water vapour, and ash.

Baking an apple pie is a physical change because the apples in the pie start changing physically and the pie crust starts hardening and rising up.

Explanation:

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.