1 . Biological systems have been doing this for __________ (billion) of years. (所给词的适当形式填空)

2 . ________________ (三分之二的学生) have taken part in the physical activity. 根据汉语提示完成句子

3 . Indeed,   his slim but strong body is just like that of millions of Chinese farmers,   to whom he has devoted his life.
确实, 他瘦削但结实的身躯, 与其为之奉献毕生的_____________无异。

4 . It took them more than one ________ (十亿) dollars to complete the project.(根据汉语提示单词拼写)

5 . Professor Yang came up with_____________________(三个解决办法) the difficult problem at the meeting. (根据汉语提示完成句子)