According to its grammatical functions, idioms can be classified into five groups. The idiom “an apple of discord” belongs to（ ）.
A、adjectival
B、nominal
C、verbal
D、adverbial
【正确答案】：B
【题目解析】：本题考查常见的名词性习语。adjectival：形容词性的；nominal：名词性的；verbal：动词性的；adverbial：副词性的。名词性习语都有一个名词充当关键词，而且在句中用作名词。an apple of discord：争斗之源，属于名词性习语。故B选项符合题意。
