题目

—Mr. Wang to Mary carefully when I entered the classroom this morning.—He is very patienthe is young.A. talking; but B. was talking ;though C. talks; though D. talked; however 答案：【答案】B【解析】句意：-今天早上王先生正在和Mary谈话，这时我进入了教室。-尽管他是年轻的，但他很有耐心。talking谈话，现在分词；was talking过去进行时；talks第三人称单数形式；talked过去式；but但是；though尽管；however然而。第一句话使用了句型be doing sth. when…正在做某事这时…，when从句中使用森林着火后，消防队员在火势的前方砍到一片树林，开辟“防火隔离带”的目的是_______________________。