Hello Mamiiixo!
Your answer should be C.
Characters who do not change during the course of a story are static. These changes include character, personality, or perspective.
In contrast, a dynamic character undergoes a major transformation in regards to their character, personality, or perspective.
By tying all the information together
I believe the answer is individuals. The drug side effect is the result of the interaction from the substance contained by the drugs and the environment in our body. It means that the effect will be influenced by the individual's age, weight, height, gender, etc.