Yerkes-Dodson law showed that every activity has its optimal motivation level, and the optimal level changes with the task difficulty. So in details, they are ( ).
A. In the low degree of task difficulty, high motivation level brings high working efficiency.
B. In the moderate degree of task difficulty, moderate motivation level brings high working efficiency.
C. In the high degree of task difficulty, low motivation level brings high working efficiency.
D. In the high degree of task difficulty, motivation level has no relationship with working efficiency.
E. In the high degree of task difficulty, high motivation level brings high working efficiency.