The Next Questions Refer to the Following Experiment

The next questions refer to the following experiment:
A researcher investigated the effect of a child's attractiveness and gender on judgments of personality and intelligence. Male teachers were shown photos of children to obtain their "first impressions" of children. Each teacher was shown four photos (the order was randomized for each teacher) : an attractive boy, an unattractive boy, an attractive girl, and an unattractive girl. The teachers rated the apparent friendliness of the child and also estimated the child's intelligence.
-This study includes the gender of of the children in the photos as

A) a manipulated variable
B) a subject variable
C) a dependent variable
D) se an uncontrolled extraneous variable