双层底设置得较高，一般可达型深的（）。
A.1/5
B.1/4
C.1/3
D.1/2
参考答案：A
If he doesn't go there, I go there, . [ ]
A. don't; too
B. don't; either
C. won't; either
D. won't; too
简述教育研究的伦理原则。
