教育家陶行知在《自立歌》中写道“自己的事情自己干，靠人靠天靠祖宗，不算真好汉”。

吃剩的饭菜放在冰箱内不容易腐败变质的主要原因是冰箱内（　　）

A．温度低，细菌繁殖速度慢

B．温度低，把细菌都冻死了

C．没有空气，细菌无法繁殖

D．温度低，营养物质分解慢

—He looks unhappy.

—Yes, but he can't say what it is ______ is bothering him.[ ]

A. as          

B. that

C. what      

D. which

根据O抗原目前将小肠结肠炎耶尔森菌分为（）

A.10多个血清型

B.20多个血清型

C.50多个血清型

D.100多个血清型

E.170多个血清型

An analyst does research about the time value of money. An investor deposits $500 million in an account that eams a stated annual rate of 3.5% for the first year and 3.0% for the second year, compounded continuously. If there are no additional deposits or withdraws, the value of the account after two years is closest to:（）

A. $519.05 million.

B. $533.58 million.

C. $536.25 million.

国境口岸卫生监督人员在执行任务时，有权对国境口岸和入境、出境的交通工具进行卫生监督和技术指导，对卫生不良和可能引起传染病传播的因素提出改进意见，协同有关部门采取必要的措施，进行卫生处理（）