Microsoft Excel was used on a set of data involving the number of defective items found in a random sample of 46 cases of light bulbs produced during a morning shift at a plant. A manager wants to know if the mean number of defective bulbs per case is over 20 during the morning shift. She will make her decision using a test with a level of significance of 0.10. The parameter the manager is interested in is:

o the mean number of defective light bulbs per case produced at the plant.
the mean number of defective light bulbs per case produced during the morning shift.
the proportion of cases with defective light bulbs produced at the plant.
O the mean number of defective light bulbs per case among the 46 cases.