分光光度计中用于可见光区的光源主要是                         。

A． To know as much as possible about the cultural differences.
B．To prepare in relevant vocabulary building, video and audio input of connected topics.
C． To translate word by word.
D． To understand thoroughly about the difference of the language systems

A.现代教学理论
B.教材的特点
C.学生和教师的经验
D.教学的实际需要