When a light is first seen on the horizon it will disappear again if the height of eye is immediately lowered several feet.When the eye is raised to its former height the light will again be visible.This process is called ().
【简答题】用所给单词的适当形式填空。 l. Please keep quiet! My sister is trying _____ (study). 2. If you want to be _____ (health), you must take _____ (much) exercise. 3. They _____ (make) a soccer next year. 4. My be...