问题
单项选择题
What is the main topic of the passage
A．The relationship between a plant's roots and its shoots.
B．What can be learned by growing roots in isolation.
C．How plants can be grown without roots.
D．What elements are necessary for the growth of plants.
答案
参考答案：A
解析：[分析] 主旨题型。 见本文主旨句，第二段第一句：The study of isolated roots has provided an understanding of the relationship between shoots and roots in intact plants．(第一段谈的是the study of isolated roots；第二段谈的是the relationship between shoots and roots)：因此选项A应为答案。