二、英语知识运用（共两节，满分45分）
第一节 单项填空（共15小题；每小题1分，满分15分）
从A．B．C．D四个选项中，选出可以填入空白处的最佳选项。并在答题卡上将该项的标号涂黑。
It was not until they came to the very spot______how serious the situation was.
A．did they realize                                                         B．that they realized
C．when they realized                                                  D．where did they realize