Consider the cladogram.

mc013-1.jpg

according to the cladogram, which organisms have roundworms as a common ancestor?
mollusks and flatworms
sponges and chordates
flatworms, sponges, and cnidarians
mollusks, echinoderms, chordates, and annelids

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.