题目

My father walked _____ in the room, looking as if he was thinking over something. A. now and then       B. up and down C. again and again      D. over and over 答案：B 解析: now and then表示时间；again and again和over and over表示次数。这三个短语都不符合语境。walk up and down in the room意思是“在房间里踱来踱去”。在室温下等体积的酸和碱的溶液，混合后pH值一定小于7的是 [     ]A．pH=3的硝酸跟pH=11的氢氧化钾溶液B．pH=3的盐酸跟pH=11的氨水 C．pH=3的硫酸跟pH=11的氢氧化钠溶液 D．pH=3的醋酸跟pH=11的氢氧化钡溶液