How do the airlines expect to prevent commercial plane crashes? Studies have shown that pilot error contributes to two-thirds of all such crashes. To address this problem, the airlines have upgraded their training programs by increasing the hours of classroom instruction and emphasizing communication skills in the cockpit. But it is unrealistic to expect such measures to compensate for pilots' lack of actual flying time. Ttherefore, the airlines should rethink their training approach to reducing commercial crashes. Which one of the following is an assumption upon which the argument depends? ['The number of airline crashes will decrease if pilot training programs focus on increasing actual flying time.', 'Lack of actual flying time is an important contributor to pilot error in commercial plane crashes.', 'Training programs can eliminate pilot errors.', 'Commercial pilots routinely undergo additional training throughout their careers.']