A clause is defined as ‘minimally consisting of a predicate of various forms’. Clauses are combined into larger units, which are loosely called sentences (Chu, 1998: 354). Thus, sentences are either simple or multiple. A simple sentence is the one that comprises a single independent clause. A multiple sentence, as suggested by its name, consists of more than one clause as its immediate constituents. It may either be a compound sentence in which the clauses are coordinated and parallel, or a complex sentence in which one or more clauses function as a clause element (such as object or adverbial) of the main clause, thus the clause(s) is (are) subordinate to the main clause. Consider:
Wǒmen shàng ge xīngqīliù yóulǎn le Xiāng Shān.
(Last Saturday we visited Fragrant Hill.)
Rúguǒ míngtiān tiānqì hǎo, wǒmen jiù qù páshān.
(If the weather is fine tomorrow, we will go to climb the mountain.)
Wǒ sònggěi dìdi yī běn wǒ cóng Běijīng mǎilái de Zhōngguó dìtú cè.
(I gave my younger brother an atlas of China that I bought in Beijing.
Sentence (1a) is a simple declarative sentence, which consists of subject, verb, object and adverbial of time. Sentence (1b) is not a simple sentence, because it contains a 如果‘rúguǒ’ (if) clause functioning as the adverbial element, so it is a complex sentence. A simple sentence, however, may have a clause within a phrase or clause element. In that case, the complexity is at the level of the phrase, rather than at the level of the sentence or clause. In (1c), for instance, the clause 我从北京买来‘wǒ cóng Běijīng mǎilái’ (I bought in Beijing) functions as a premodifier of the complex NP 中国地图册‘Zhōngguó dìtú cè’ (Chinese atlas), which is the clause element object, hence such a sentence is still a simple sentence.
 Loar, J. K. (2011). Chinese syntactic grammar: functional and conceptual principles. New York: Peter Lang.