Answer: c) color of the carton
Explanation:
Independent variable in research and experiment is defined as the variable or factor that can be altered or change accordingly to observe the results and impact on dependent variable.
According to the question, carton's color is the independent variable as there are green and red colored carton i.e change in carton's color is made to observe the rating of participants.
Other options are incorrect because participants gender, rating of participant and ice-cream flavor are not the factors that are independent in research.thus,the correct option is option(c).