Researchers want to test the effectiveness of three different types of COVID-19 vaccines and each individual can only receive one type of vaccine. Why would it not be possible to conduct a one-way within-groups ANOVA? a. The same individuals could not participate in each level of the independent variable (i.e., they could not receive each of the vaccines). b. There is only one independent variable. c. There are two independent variables. d. There are three levels of the independent variable (i.e., three types of vaccines)