Which one of the following statements accurately describes a characteristic of red blood cells?
a. they transport oxygen to all the cells of the body.
b. they're agents of inflammation.
c. they lack hemoglobin.
d. they're convex disks with a large nucleus.

What sentence best supports the statement that hormones are involved in the regulation of homeostasis? a. the hormone erythropoeitin increases the production of red blood cells when oxygen levels are low. b. the hormone oxytocin promotes labor contractions of the uterus during childbirth. c. the hormone melatonin induces sleep and its production is slowed by exposure to light. d. the hormone cortisol suppresses the immune system and is produced when the body is under stress.