Which of the following is true regarding expression levels of clock genes in the suprachiasmatic nucleus of the hypothalamus (scn)?
a. Per and Tim protein levels are high early in the morning, stay constant throughout the day, and drop through the night
b. Per and Tim protein levels are low early in the morning, stay constant throughout the day, and rise through the night
c. Per and Tim protein levels are high early in the morning, drop throughout the day, and rise through the night
d. Per and Tim protein levels are low early in the morning, rise throughout the day, and drop through the night