1. Boyd/Usilton

2.  1. If an animal is a robin, then the animal is a bird.  2. If an angle measures 130, then the angle is obtuse.  3. Vertical angles have a vertex.  4. Dolphins are mammals.

3.  1. If a woman is born in Florida, then she is American.  2. If a number is divisible by 3, then it is odd.  3. If a month has 28 days, then it is February.  4. If two angles form a linear pair, then they are supplementary.

4.  1. A leap year is a year that has 366 days because one day is added to the month of February.  2. A light bulb gives off light and is hot to the touch.  3. Opposite rays are two rays that share the same endpoint.  4. Linear pairs of angles are two adjacent angles that share one side, and the sides they do not share are opposite rays.

5.  If the converse is true and the statement can be written as a biconditional the definition is a good definition.  If the converse is false or you can find a counterexample, the defintion is not a good definition.