学习目标：让学生掌握第四单元的单词及短语发音、拼写及中文意思。
学习重点：第四单元单词表中的黑体单词及短语。
学习难点：掌握以下单词及短语预习案：atmosphere, multiply, satellite, unlike, climat, gravity, theory, crash, spaceship, pull, fundamental, chain, astronomy, atom, in time,
lay eggs, cheer up, give birth to, in one’s turn, break out, prevent...from, now that,watch out
预习案
I. Read the new words and expressions in Unit4 and try to master the black words and expressions.
