单选题 ______ that my head had cleared, my brain was also beginning to work much better.

【正确答案】 B

【答案解析】[解析] 本题考查固定搭配的用法。now that为固定搭配，引导原因状语从句，意为“既然”，符合句子意思，故选B。句意为：既然我思绪清晰了，大脑也开始更好地工作了。