13，动机最佳水平应是______程度的激活或唤起，此时对学习具有最佳效果。
参考答案：中等
Karin found some waste paper on the floor,she _____ it ______ and threw it into the dustbin(垃圾桶).
[ ]
A. put; up
B. picked; up
C. turned; up
D. looked;up
《尚书》
