What is not a common purpose for a research report?

a. to show cause and effect

b. to persuade

c. to entertain

d. to predict

The correct answer is: to entertain.

It is generally never, or very rarely, a purpose of a scientific activity to entertain. Sometimes, some scientific writing can be made to be a little entertaining to increase the interest in the work, but it is never its main purpose - and it is generally not widely accepted to make a scientific report entertaining.