Answer:The cost of skiing is Studying the Library.
Explanation:Studying at the Library is what you are currently considering to do as a priority.Sacrificing your studies at Library is the price you have to pay in other to go skiing. That is your forgone alternative or the opportunity cost of skiing .This simply means,you have list of things to do on Saturday as a priority but one seems more important to you than the other.Since you cannot do the two on that same day,you will have to sacrifice one for the other.Sacrificing your studies at the Library is the price you have to pay to go skiing.