Which is not an observation?
a. the mouse is eating.
b. the mouse is hungry.
c. the mouse has grown 2 cm.
d. the mouse has consumed 15 ml of water.

because natural gas is colorless, odorless, and tasteless, distributors add mercaptan (a chemical that smells like sulfur) to give natural gas a distinct unpleasant odor (it smells like rotten eggs). they locate the types of rock that are likely to contain natural gas deposits.