When only one adjective acts as a predicate, the sentence should be a sentence of greetings, a yes-no question, a special question, an answer to the special question or a sentence of comparison, e.g.

• 由单个形容词充当时，要有一定的语用条件：用于问候、用于是非疑问句、用于特指疑问句及其答句或用于对比。