Robinson Manipulates Two Variables in His Experimental Investigation of Test-Taking

Robinson manipulates two variables in his experimental investigation of test-taking performance: the number of participants seated in the room and the room temperature. He finds that regardless of the temperature in the room, participants do better on the test when the room is less crowded. Which of the following statements about this study is true?

A) There are two independent variables in this study.
B) There is one independent variable in this study.
C) There are two dependent variables in this study.
D) none of these