答案：D

题目分析：考查not until在强调句中的用法区别。强调句型的基本结构是：It is/was + 被强调部分 + that/who/whom + 句子未被强调部分。该句型的最大特点是：去掉it is/was和引导词that/who/whom之后，剩下部分为完整的一个句子（有时候需要调整句序）。如：I met him in the street yesterday.强调主语I时，改为：It was I who/that met him in the street yesterday.如果去掉被it was和引导词that/who/whom外，适当调整句序后，都会还原成原句：I met him in the street yesterday. 而not...until...的强调句型为：It is/was not until + 状语/状语从句 + that + 句子/主句的肯定句形式。如：I didn't go to bed until my parents returned.其强调句型为：It was not until my parents returned that I went to bed. 故D正确。