How many cells are there in the human body?

Explain how fossils scientists make discoveries about the lives of organisms and about how environments have changed over time. plz hurry up it time

The third stage of cellular respiration is (2 points)

Which of the following best describes the purpose of the parathyroid hormone? a. it decreases the blood calcium level and decreases blood phosphorus level. b. it decreases the blood calcium level and increases the blood phosphorus level. c. it increases the blood calcium level and increases blood phosphorus level. d. it increases the blood calcium level and decreases blood phosphorus level.