The correct answer is B. Cognitive coping training
Step-by-step explanation:
In a research study or experiment, the independent variable can be identified by answering questions such as what is the variable the researcher manipulates? or which variable is expected to affect another?. In Dr. Green's study, the factor she is manipulating is cognitive coping training because half of the participants are exposed to this training, and the other half are not exposed.
Also, the purpose of this study is to "examine the effect of cognitive coping training on stress levels", which shows cognitive coping training is independent as this is not affected by other variables and it is expected it affects the second variable or stress level. According to this, her independent variable is cognitive coping training.