单项选择题
A．the study of the universe B．a Comparison C．the study of light waves D．the result of scientific investigation
A. Hardly ever. B. No wonder you look so well. C. Follow my advice. D. I’m sure. E. Do you want to go with me F. Right on! G. Have a nice day. H. That’s too bad.
A．they make us think about our universe B．they were used to represent some other phenomena C．they are more precise than theories D．they indicate further direction and help us make predictions