Which of the following is transparent（）

单项选择题The title that best expresses the ideas of the passage is （）

A．"Why are there shadows"
B．"The transparent materials"
C．"How to cast a shadow"
D．"Shadows and light waves"

单项选择题An opaque material is （）

A．a material that can be seen through
B．a translucent(半透明的) material
C．a material that can not be seen through
D．a lucent material