Answer: B) Altering.
Explanation: Context clues are hints that an author gives to help define a difficult or unusual word within a book. They can be placed within the same sentence as the word to which it refers or it may follow in the next sentence. In the given passage, the context clues that help to identify the definition of the word "variable" are "inconstant" and "changes" from which we can infer that the word "variable" means "altering."