With reference to the theoretical and psychological analysis of Learning Curves and Plateaus in Learning, which of the following statements presents the most accurate combination of the causes of a 'plateau' and the characteristic of a 'Convex Curve' (Negatively Accelerated Curve)?

When the speed of learning stops for some time or there is no improvement in performance in the learning process, it is called a plateau in learning, the main causes of which include fatigue, lack of motivation, complexity, and improper teaching methods. In addition, a convex or negatively accelerated curve shows that the speed of learning is fast at the beginning, but as the task becomes more complex, the rate of improvement slows down with practice.