对铜绿假单胞菌作用较强的药物是（）。
A.林可霉素
B.妥布霉素
C.四环素
D.氯霉素
E.红霉素
参考答案：B
贾谊的代表作《（）》开了中国古代散文单篇“史论”的先河。史论以历史事实作为论说的对象，从中得出结论。“前事之不忘，后事之师也。”就是出自于该文。
Suppose you were taken good care of by Mr.Smith when you visited Beijing where he lived. Write a letter in about 100 words to extend your appreciation. Do not sign your own name, using "Li Ming" instead. Do not write the address.
