Answer
You would look for evidence of circadian patterns in either post translational protein modification, which would alter CO activity by adding or removing things like phosphate groups, or in protein distruction, which would modify activity by destroying CO protein at certain times of the day.
Work Step by Step
This question is asking you to connect this chapter with earlier material on gene expression and regulation of protein activity. Review those chapter briefly and you will see the two kinds of regulation mentioned in the answer.
