写作三：从稳定核心句逐层扩展

写作能力三：先写稳定核心句

复杂句不是高分前提。先确保一句话有明确主语、限定谓语和完整对象，再增加原因、条件或让步。本课只训练从核心命题扩展一句。

自拟命题

核心：Feedback improves learning.

第一层加入机制：Feedback improves learning because it reveals specific weaknesses. 第二层加入条件：Feedback improves learning when it identifies a weakness and suggests a practical next step.

每次只加一个逻辑模块，检查主谓一致、时态和指代。不要把 because、which、although 同时堆进一句。

反例与修订

错误：Feedback which useful and students can know weakness improve learning.

逐步修订：补系动词 which is useful；明确主句主语谓语；把并列关系改成原因：Useful feedback improves learning because it helps students identify their weaknesses.

错解反馈

若句子越改越长却找不到主谓，说明扩展顺序错了。回退到核心句，再加一个从句。

正文练习

从 Libraries support communities. 扩成含一个原因从句的句子。

**参考：**Libraries support communities because they provide reliable information and shared learning spaces.

独立验收

任选一个主题写“核心句→一次扩展→校验表”，标出主语、谓语、连接词和新增逻辑。