题目

I had just nodded off to sleep __________ I was woken up by an almighty crash from their house. A． when B． what C． why D． that 答案：A【解析】 【详解】 考查固定句型。句意：我刚睡着，就被他们房子发出的一声巨响吵醒了。此处为句型 had just done when...，表示 “ 刚一 …… 就 ……” 。故选 A 。化符号中表示2个氢原子的是                                           （      ）      A. H             B. 2H             C. H2              D. 2H2