________ leave home voluntarily for at least one night, without parental permission

One day in class, Josef began to sweat and feel short of breath. He was suddenly dizzy and afraid he would pass out. Even though he had no heart issues, Josef felt as if he were having a heart attack. There seemed to be nothing that triggered Joseph having this experience. The disorder that BEST describes what Josef is experiencing is:

Which of the following would limit the effectiveness of the experimental method?

a) random assignment b) selection bias c) independent variables d) representative samples