Which hypothesis fails to meet the criteria of testability?

Which hypothesis fails to meet the criteria of testability?
 
  a. Proper handwashing prevents the spread of infection.
  b. Consistent practice of low-impact aerobic exercise will increase coordination among older adults.
  c. Patients who used guided imagery during magnetic resonance imaging (MRI) procedures will have reduced perceptions of emotional distress compared with patients who do not use guided imagery during MRI.
  d. Postoperative patients who receive around-the-clock scheduled analgesics will have lower levels of pain compared with postoperative patients who receive analgesics on an as-needed (PRN) schedule.