I didn't realize how special my mother was until I became an

主语i,be动词加relize做谓语,how引导从句作宾语,倒装,until引导时间状语从句
再问： 那do是助动词吧
再答： 恩，我写错了，助动词do加relize作谓语，这个句子的肯定语气是 I realize my mother was special when i became an adult.这里when引导时间状语从句，not until是否定语气引起表语部分倒装how special（表语） my mother was