A (n) is a group of words whose meaning is different from the meaning of each word understood on its own.
A：idiom
B：sentence
C：grammar
世界上最大的岛屿是（ ）
植物的根尖是植物吸收____ 和____ 的主要部位，它包括四个结构，从最前端开始依次是根冠、____ 、伸长区和 ____ 。
They considered ______ a computer ,which was considered ______ a great help in their work.
