单选题 It was not until she got on the bus ______ she remembered she had left her key at home.
【正确答案】 C
【答案解析】[解析] 本题测试的是强调句结构的用法。该结构是由“it is/was+被强调部分+that/who ...”构成,被强调的部分可以是句子的主语、宾语或状语。因此本题答案为C。