Answer: A) to entertain the reader with a humorous story.
Step-by-step explanation: when writing, an author can have different purposes, like to entertain, to persuade, to inform, to criticize, etc. In the given excerpt from a letter, we can see a story that has the purpose of entertain, because it is a funny story about how the speaker brought her skis closer together and they criss-crossed making her ski backward. So the correct answer is the corresponding to option A.