桑代克认为尝试——错误学习的基本规律有：效果律、练习律和______________。
参考答案：效果率
The American president who____the freedom of slaves was shot to death. [ ]
A. fought with
B. fought for
C. fought against
D. fought back
过滤器在运行过程中会出现流量不够的原因？
