Which best describes the big bang theory? a. the universe is 4.6 billion years old. b. the universe is shrinking. c. our universe is not the only universe. d. the universe is expanding.

the endocrine system secretes hormones into blood and other body fluids. these chemicals are important for metabolism, growth, water and mineral balance, and the response to stress. hormones provide feedback to the brain to affect neural processing. reproductive hormones affect the development of the nervous system.

covalent bonding is a form of chemical bonding between two non metallic atoms which is characterized by the sharing of pairs of electrons between atoms and other covalent bonds.