Which of the three cells, if any, has the greatest surface-area-to-volume ratio?
a. the cell with radius 1
b. the cell with radius 2
c. the cell with radius 3
d. All three cells have the same surface-area-to-volume ratio.

In an experiment examining the effects tai chi on arthritis pain, callahan (2010) selected a large sample of individuals with doctor-diagnosed arthritis. half of the participants immediately began a tai chi course and the other half (the control group) waited 8 weeks before beginning. at the end of 8 weeks, the individuals who had experienced tai chi had less arthritis pain that those who had not participated in the course.