题目

综合填空 阅读下面的短文，根据每个空格中所给的词首字母填入适当的词，使短文意思完整。 This morning a crowded train was travelling south towards London . When it was traveling at 60 miles an hour , a carriage caught fire . Black s    （1）came from under the carriage . On English trains there is a steel chain . When someone pulls the chain , the train will come to a s    （2）. When the passengers saw the fire and the smoke , one of them q    （3）pulled the train . As the train was s    （4）down , people opened the doors and j� 设函数在其定义域上的取值恒不为，且时，恒有．若且成等差数列，则与的大小关系为（   ）   A．  B． C．  D．不确定