Why are chromosomes found in pairs in most organisms?

Which kind of worm has a closed circulatory system? a planarian b fluke c pinworm d an earthworm

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.

The most famous fossil called archaeopteryx is which of the following? a dinosaur a fern a fish a bird