Identify independent and dependent variables

Identify independent and dependent variables in the studies described below:
A) Dr. X does a study with three groups of ten students each. Each group consumes a different amount of caffeine (high, medium, and low amounts). Dr. X then measures all of the students on how well they do on a concentration test.
B) A researcher interested in the relationship between social media use and mood. They randomly assign half of the participants to browse their favorite social media app for 5 minutes, while the other half of the participants are asked to do nothing for 5 minutes. Then, all participants complete a questionnaire that measures their mood.
C) Students at a University were split into two groups and each received a different text for a psychology course. One group received a traditional textbook, while the other received an interactive textbook on a tablet computer. After the course, the final exam grades between the two groups of students were compared.