Which statement about the experiment of lttborato

Which statement about the experiment of lttboratory rats is correct?

A.One group was exercised by running circles inside.

B.One group was exercised in a complicated obstacle course outside.

C.The animals that learned to go through the obstacle course exhibited a greater number of brain cells than the animals in the exercised or inactive groups.

D.The animals that exercised inside the automatic wheel possessed a greater density of blood vessels in the brain than did either of the other two groups of animals.