unit 4 第一课时 ⅰ.单词拼写 1．this ________ (理论) is helpful to explain how the universe began. 2．the big project has cost almost as much as one ________ (十亿) dollars. 3．two people have been killed in the ________ (暴力的) incident on march 2nd. 4．across the ________ (地球), sea level varies by hundreds of f
