*Question*: A change in the environment that causes a response is known as a OPTIONS:
- stimulus
- habit
- reflex
- source
*Answer*: stimulus

*Question*: Comparing the skeletons of which of the following fish would best show the evolution of a fish species? OPTIONS:
- a male fish and a female fish that could produce offspring
- the same fish just before it received a cut and after it healed
- a fish that lived recently and a fish that lived a long time ago
- the same fish just after it hatched and when it was full-grown
*Answer*: a fish that lived recently and a fish that lived a long time ago

*Question*: What is the smallest unit of an element that still has the properties of that element? OPTIONS:
- an atom
- a compound
- an electron
- a molecule
*Answer*:
an atom