What is sometimes referred to as the “master gland” because the hormones it produces controls growth, reproductive cycles, and several other functions?
a. pituitary gland
b. parathyroid gland
c. thyroid gland
d. sebaceous gland

Which of the following is a reason why early living organisms on earth could not have survived on the surface? 1. the lack of an ozone layer 2. the lack of oxygen in the atmosphere 3. the fact that these organisms were single-celled