根据哈桑的语类结构潜势理论，语类结构由必选成分和可选成分及其重复成分和顺序组成。
According to Hasan's generic structure potential theory, a generic structure is constituted of the obligatory elements, the optional elements, their recursive elements and their sequence.
存在三类权限请求：必选、可选和被拒绝。
Three kinds of permission requests exist: required, optional, and refused.
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