Unless the author makes it clear that citation is not allowed, as long as it is a published paper or book, it can be cited, as long as the source is clearly indicated.

Quoting refers to the rhetorical method of quoting ready-made words in speech or writing, such as poems, aphorisms and idioms, to express thoughts and feelings. Citation can be divided into explicit citation and implicit citation. Explicit quotation refers to quoting the original text directly with quotation marks, or only quoting the main idea of the original text without quotation marks, but indicating the source of the original text.