T细胞特异识别抗原的物质是（） A.IL-2R B.FcrR C.SRBCR D.T

The other day we traveled fifteen hours to a magic country. which     America,and we enjoyed ourselves

there for a month. [ ]

A. was called      

B. is called        

C. had been called      

D. has been called

阅读下面短文，根据括号内所给汉语写出单词的正确形式（每空一词）。

Have you ever heard of Jet Li? He is a great film   小题1:     (明星) in China. His action films are very popular in the小题2:   （世界）because he is good at Kung Fu. Many of us like him. “ Huo Yuanjia” is one of his   小题3:   （最好的） films. It’s an action film. In this film, there are many famous  小题4:  （演员）and actresses. I 小题5:  认为）it is very exciting and funny. It’s    小题6:  （真正地）a good film, and  小题7:  （所有）of us like it. At the  小题8: （相同的）time, Jet Li is a kind man. He donated much money to the people in Sichuan   小题9:    （在.....之后）the earthquake on May 12th, 2008. He would like to   小题10: （建造） some new schools for the children there.

单位阶跃信号ε（t）是物理量单位跃变现象，而单位冲激信号δ（t）是物理量产生单位跃变什么的现象？（）

A.速度

B.幅度

C.加速度

D.高度

心绞痛与急性心梗心前区疼痛的区别之一是

A．心绞痛更重
B．心绞痛更持久
C．心绞痛发生无诱因
D．心绞痛多伴高血压
E．含硝酸甘油有效

处理井下事故用常备工具有哪些？