Answer:
lack of reproduction
Step-by-step explanation:
Attention refers to whether Betty was paying attention to her sister or not. We learn that Betty watched her carefully, so this is not the problem. If the problem was retention, it would mean that Betty is unable to remember what her sister did. However, we know that this is not the problem either. Lack of motivation would mean that Betty is not willing to do what is necessary to achieve the move, but we know Betty has practiced for more than an hour. The problem is lack of reproduction, which tells us that Betty simply cannot do the move in the exact same way her sister can.