题目

One day an American friend invited me to a party． It wasn’t a real party, it was some kind of informal get-together． Since it was summer time, he had a cookout where most of his American friends and relatives were known to me, but there were others I had never met before．        It was the most embarrassing （令人尴尬） party for me when I noticed that everybody was wearing jeans and simple T-shirts for the day, while I arrived in proper dress with my shoes and my hair all fixed for a fancy party．It was hard to explain my embarrassment to other guests．When one of them t需借助其它物质才能鉴别的一组物质是（　　）A．浓盐酸和浓硫酸B．氧化铜和氧化镁固体C．氧气和氨气D．烧碱溶液和澄清石灰水