【正确答案】 C

【答案解析】 强调句。本题综合考查了not...until...和强调句的用法。本句正常语序为She did not wonder if she had made a mistake until long afterwards. 可以将not until放在句首，此时主句部分倒装，变为Not until long afterwards did she wonder if she had made a mistake. 还可以再加上It was...that...结构将此句变为强调句，但是由于此时not until不再位于句首，故主句不需倒装。