Nine Answer Keys include answers for all student exercises, including tests. The Answer Keys for LightUnits 301-307 are the same as the LightUnits but have the answers filled in. The answers for LightUnits 308-310 are presented in a list format rather than matching the format of the LightUnit. Answers for LightUnits 309 and 310 are combined into one book. Test answers are located in the center of each Answer Key, allowing them to be easily removed and filed to prevent student access.