填空题
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
Paragraph 2（）
A
单项选择题 Oklahoma is an area often experiencing natural disasters.（）
单项选择题 The earthquake is the most unpredictable natural disaster.（）
单项选择题 He kept in constant contact with his family while he was in Australia
