Radiation And Cross Country

We learned about radioactivity this week. I'm really confused about this section because I missed a block day to go to a cross country meet. This caused the week to be extremely difficult for me to keep up with all the things that are going on in chemistry. It is very confusing when I go into class and we go over things that I've never heard of before. The cross country meet was very hard but i surprised myself since I did so well.