Refer to the Figure

Multiple Choice

Refer to the figure.
This figure shows the hourly changes in the production of messenger RNA (mRNA) encoded by the PK2 gene in mice exposed to a light-dark cycles of 12 hours of light and 12 hours of darkness (LD) , complete darkness for 2 days (2DD) , and complete darkness for 8 days (8DD) . How do these results support the hypothesis that PK2 is a clock messenger?

A) The production of PK2 depends on the amount of daylight that is available.
B) PK2 is produced in a circadian pattern independent of light-dark cues.
C) A mutation in certain key clock genes disrupts the circadian rhythm of PK2 production.
D) Prolonged periods of darkness increase the expression of the gene that produces PK2.