Tell whether each of the following relationships reflects a positive or a negative correlation:
a. the amount of stress in people's lives and the number of colds they get in the winter
b. the amount of time that people spend suntanning and a dermatological index of skin damage
c. happiness and suicidal thoughts
d. blood pressure and a person's general level of hostility
e. the number of times that a rat has run a maze and the time it takes to run it again.