Unit 4 Exploring plants
Part 2 Teaching Resources
第二部分教学资源
Section 2 Notes to difficult sentences from Unit 4
Exploring plants
1． Collecting “exotic” plants，as they are called，dates back t o the earliest times．收集 “异国”植物，人们这样称呼他们，可以追溯到远古时期。
句中as they are called是非限制性定语从句，as是关系代词，起连接作用，同时作从句中的主语补语。请看关系代词as的其它例句：I received the same grade as you did. Those as want to can come with me. I received the same grade as you did. Those as want to can come with me.
2． However，it was not until the eighteenth and nineteenth centuries that the exploration of
the botanical world began on a large scale．然而，直到十八、十九世纪植物学世界的探险活动才开始大规模进行。
句中it was not until…that…意思是：在...以前一直(不...),...以后才。例如： It was not until he was thirty that he started to paint. 他直到三十岁才开始绘画。
