Heart disease and stroke are only a leading cause of death in industrialized countries, but not a concern in developing and underdeveloped countries.​

Research by Kiecolt-Glaser and her colleagues has shown that Alzheimer's caregivers, compared with other people of the same age and gender,​

A) had poorer psychological and physical health.​
B) ​had lowered immune system function.
C) ​more quickly recovered their own health after the death of the Alzheimer's patient.
D) ​both a and b are correct.

Which of these is NOT a function of a useful theory?

A) Generating research
B) Being a guide to action
C) Eliminating researcher bias
D) Organizing research observations