Questions Below Will Be Based on the Following: a Researcher

Questions below will be based on the following: A researcher wishes to test the hypothesis that intelligence is a sex-linked characteristic. A random sample of 1000 women is selected and given IQ tests. Similarly, a random sample of 1000 men is selected and also given IQ tests. The mean IQ's of the two groups are compared and the difference is found to be significantly in favor of the females.
-In this study, the variable being manipulated by the researcher is

A) sex
B) intelligence
C) the IQ tests
D) none of these