问题补充：
—Mr. Li to Mary carefully when I entered the classroom this morning.
—He is very patient he is young.
A. talking; but
B. was talking; though
C. talks; though
D. talked; however
答案：
A. talking; but
(答案→)B. was talking; though
C. talks; though
D. talked; however
解析：句意：今天上午当我进教室时，李老师正在与玛丽认真地交谈。尽管他很年轻，他很耐心。talk to与……交谈；根据when I entered the classroom this morning.今天上午当我进教室时，时间状语从句为一般过去时，主语正在发生某事，为过去进行时；though尽管，but但是，however然而；年轻是耐心的让步状语，故选B.
