A sudden, irresistible urge to sleep, which lasts a few minutes to half an hour during the daytime, is called

The specific color that an eye perceives - such as red, green, and blue - is referred to as __________

a) brightness. b) contrast. c) hue. d) saturation.

The hormone melatonin is produced by the ________ gland

a. pituitary b. pineal c. adrenal d. thyroid