* a) No baseline risk is given, so it is not know whether a a high relative risk has practical importance

* b) High relative risk has practical importance

* b) A confounding variable rather than the explanatory variable is responsible for a change in the response variable.

* c) The direction of the relationship between two variables changes when the categories of a confounding variable are taken into account.

* d) The results of a test are statistically significant but are really due to chance.

Answer - c