【正确答案】：
IDIOMS CAN BE CLASSIFIED INTO FIVE GROUPS.
(1) IDIOMS NOMINAL IN NATURE；
(2) IDIOMS ADJECTIVAL IN NATURE；
(3) IDIOMS VERBAL IN NATURE；
THIS IS THE LARGEST GROUP OF ALL. THE STRUCTURES OF SUCH IDIOMS ARE QUITE COMPLEX AND THUS CAN BE SUBDIVIDED INTO PHRASAL VERBS AND OTHER VERB PHRASES.
(4) IDIOMS ADVERBIAL IN NATURE；
(5) SENTENCE IDIOMS. THEY EMBRACE DECLARATIVE, INTERROGATIVE, IMPERATIVE AND EXCLAMATIVE SENTENCES. IN TERMS OF COMPLEXITY THEY CAN BE FURTHER DIVIDED INTO SIMPLE, COMPOUND AND COMPLEX SENTENCES. 
【题目解析】：Idioms can be classified into five groups. (1) Idioms nominal in nature； (2) Idioms adjectival in nature； (3) Idioms verbal in nature； This is the largest group of all. The structures of such idioms are quite complex and thus can be subdivided into phrasal verbs and other verb phrases. (4) Idioms adverbial in nature； (5) Sentence idioms. They embrace declarative, interrogative, imperative and exclamative sentences. In terms of complexity they can be further divided into simple, compound and complex sentences.
