In the Oral Approach, Palmer insisted that there was a basic difference between the spontaneous capacities of human beings to ______ language naturally and unconsciously and the trained or"situational" capacities of the classroom learner which allowed him to learn language consciously.

气相与液相（）不同，使气液两相分界面会看得很清楚，反射式液位计由此测量液位

A、颜色

B、折光率

C、透明度

D、反射率