急性脓胸在病程上超过几周为慢性脓胸（）。
A.3周
B.6周
C.12周
D.24周
E.48周
参考答案：B
The teenager seemed to be a good driver; _____, I didn't dare to travel in his car. [ ]
A. therefore
B. so
C. even though
D. even so
我国将纳税人分为一般（）和（）两大类。
