A. How is the nature of light explained today
B. What are sources of light
C. How did physicists measure the speed of light
D. How does light travel
E. How did people think of light years ago
F. What causes a shadow

Some instances such as reflection and absorption can change（）

A．It is the thinnest material in the world.
B．It is made of the most abundant elements in the world.
C．It can help to make electronic components smaller.
D．It helps engineers to produce more sensitive electronic products.

A．Some animals possess unique skills.
B．Many inventions get ideas from nature.
C．People should protect nature.
D．Bionics is far from perfect.