就给定资料所反映的主要问题，用1200字左右的篇幅，自拟标题进行论述。要求中心明确，内容充实，论述深刻，有说服力。
参考答案：略。
— You look so young. Haven't you graduated from your university?
— Yes. I _____ in the English department of Yunnan University for four years. [ ]
A. had studied
B. has studied
C. studied
D. was studying
诊断时进行鉴别诊断的疾病是
A．膝关节结核
B．膝关节交叉韧带损伤
C．膝半月板损伤
D．化脓性关节炎
E．Ewing瘤骨肉瘤膝关节骨折
