Researchers want to know if taking increasing amounts of ginkgo biloba will result in increased capacities of memory ability for different students. They administer it to the students in doses of 250 milligrams, 500 milligrams, and 1000 milligrams daily, for one month. At the end of the month the students were asked to complete a memory test and researchers recorded the amount of points each student scored. The researchers want to use amount of ginkgo biloba to predict memory test score therefore, the explanatory variable in this study is the amount of ________ ______. Be sure your answer is spelled correctly, if necessary copy and paste from question into answer box.