Which best describes the results of this experiment

This is a coral reef ecosystem. many biotic and abiotic factors affect the health of this ecosystem. which set correctly pairs a biotic factor and an abiotic factor?

Explain how paleontologists use trilobite fossils as index fossils for various geologic time periods.

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.