It was not until mid-night ________ he went back home after the experiment.
A. when B. /
C. that D. before
It was not until mid-night ________ he went back home after the experiment.
A. when B. /
C. that D. before
【解析】选C。考查强调句型。句意：直到半夜他才做完实验回家。“not. . . until”的强调结构为：It is/was not until. . . that. . . 。故正确选项为C。