圆的周长总是直径的______倍，我们把它叫做______，计算时通常取____

I have ___________ orange.[ ]

A. an

B. a

C. three

Haisong Jiang, who slipped (偷偷溜进) past a security checkpoint(安全关卡) on Jan. 3, causing a shutdown of Newark Airport, tried to apologize for his mistake.

" I feel guilty about this serious mistake. At that moment, I was very excited with my girlfriend, and I didn't think too much," Mr. Jiang, 28, said Tuesday in his first interview since causing the six-hour shutdown at the airport.

On Tuesday, Newark Municipal Court judged that besides the community service, he must pay a $500 fine (罚金) and $158 in court fees. In an agreement between the court and Mr. Jiang's lawyer, Mr. Jiang will pay off his money punishment all by community service instead.

　　Haisong Jiang, a native of China, about a year ago moved to the United States in 2004 to study and met his girlfriend, also Chinese and 26. She has since moved to California.

The lovebirds did the town over the Christmas holidays: shopping in SoHo, visiting the tree at Rockefeller Center, celebrating New Year's Eve in Times Square - the works. On Jan. 3, he watched her pass through security, but he wanted to spend more time with her. When he noticed the officer leave his post, he saw his chance, he said. He slipped under the rope and kissed her and, arm in arm, walked her to her Continental Airlines gate and saw her onto the jetway. "And immediately I left," he said.

　　Three days passed. "Friday, the police found me," the future scientist said. He was at the gym when his roommate called to say two police officers were at their home. "It's not right to enter the airport. Immediately I know the police want to ask me this thing."

　  He expects to serve half of his community service in a soup kitchen - "I like to cook" - and the other half in a hospital. He plans on moving to California to be with her and work in a laboratory after completing his degree in May or June.

He never types his name into search engines on the Net: the number of hits is shocking.

What’s the best title of the passage?

A. A moving love story  B. An escape from security check

C. A kiss causing great trouble      D. When a man loves a woman

How much did Mr. Jiang finally pay for his mistake?

A. nothing      B. $ 500  C. $158   D. $ 658

Which of the following sentences is true?

A. Mr. Jiang was sent to the police station right after he went out of the airport.

B. The lovebirds spent their Christmas holidays in California.

C. Mr. Jiang caused so much trouble on purpose.

D. On Friday, the police didn’t find Mr. Jiang at his home at first.

What can you infer from the passage?

A. Mr. Jiang is an American-Chinese.

B. Mr. Jiang and his girlfriend’s love story has finally ended.

C. Many people have known about Mr. Jiang on the net.

D. Mr. Jiang will become a scientist with certainty.

某实验小组对中学课本中可生成氢气的反应进行了研究，总结出三个可以生成H₂的反应：①Zn+盐酸②Na+水③Al+NaOH溶液。请回答下列问题：

(1)写出②、③反应的离子方程式②________________；③________________。

(2)在点燃H₂之前必须先进行__________________。

(3)实验小组在点燃用上述装置制得的H₂时，①③实验获得成功，②却失败了。他们分析认为失败的原因是Na与H₂O的反应速率太快，Na的用量太少。于是他们准备增加钠的用量，可老师说太危险，你认为产生危险的原因是_____________。

(4)实验小组查阅钠、苯、水的密度分别为0.97g/mL、0.88g/mL、1.00g/mL，并据此对实验进行了改进。在改进后的实验中H₂的生成速率减慢。 原因是________。改进后的实验现象为_________________________________________。

塔的起源和演化是怎样的情况

以下哪个生育期是小麦田间花期检验的最佳时期？（）

A、出苗期

B、拔节期

C、抽穗期

D、灌浆期