下列物质的鉴别方法中正确的是（ ）

A．MnO2和木炭——观察颜色

B．CO2和N2——燃着的木条分别伸入瓶中

C．Ca（OH）2溶液和稀盐酸——取样，滴加碳酸钠溶液

D．NaOH溶液和Na2CO3溶液——取样，滴加酚酞试液

A young woman carrying a three-year-old child got on a bus. The conductor hurried to give her a warm welcome and then kindly asked the other passengers to make more room for the woman and her child. On seeing this, people began to talk. "You know this conductor used to be very rude. Now suddenly he has changed his bad behavior, "said a middle-aged man.
"Yes, he should be praised and we must write a letter to the company," said a second passenger. "That's right," another lady said, "I wish a newspaper reporter were here so that more people could learn from this conductor.”
Just then a gentleman who looked like a teacher turned to the conductor and said, "Excuse me, but can I know your name, please? Your excellent service must be praised..."
Before he could open his mouth, the three-year-old child sitting on the young woman's lap interrupted, "I know his name. I call him Dad."
【小题1】
One passenger suggested writing a letter to the company to ______  .

A．make a demand for more buses	B． thank the conductor for his good service
C．criticize the conductor for his rude behavior
D．invite a newspaper reporter to write about the conductor

【小题2】
What was the gentleman?

A．A teacher.	B．A newspaper reporter.
C．Not known from the story.	D．The conductor's friend from his company.

【小题3】
. The word "he" in the last paragraph refers to _______.

A．the gentleman	B．the conductor
C．the middle-aged man	D．the three-year-old child

【小题4】
It is clear from the story that the conductor _______.

A．has changed his attitude towards his work

B．has now been kind and polite to all passengers

C．has not changed his rude behavior to passengers

D．has now been kind and polite to women with children

如图所示，空间分布着宽为L，垂直于纸面向里的匀强磁场．一金属线框从磁场左边界匀速向右通过磁场区域．规定逆时针方向为电流的正方向，则感应电流随位移变化的关系图（i-x）正确的是

如图所示，空间分布着宽为L，垂直于纸面向里的匀强磁场．一金属线框从磁场左边界匀速向右通过磁场区域．规定逆时针方向为电流的正方向，则感应电流随位移变化的关系图（i-x）正确的是

如图所示，空间分布着宽为L，垂直于纸面向里的匀强磁场．一金属线框从磁场左边界匀速向右通过磁场区域．规定逆时针方向为电流的正方向，则感应电流随位移变化的关系图（i-x）正确的是

珠江三角洲曾遭遇“咸潮”，水源中含氯量高达7100mg/L，远远超过正常值250 mg/L。以下说法正确的是（   ）

A．“咸潮”中氯离子浓度可达0.2mol·L—1

B．自来水厂可加入适量AgNO3溶液除去Cl—

C．自来水厂可用蒸馏法来净化水

D．直接用“咸潮”水作为水源，对人体无害

如图，在中，分别是的中点，若，Co则  cm．

如图，在中，分别是的中点，若，Co则  cm．

如图，分别以△ABC的两条边为边做平行四边形，所做的平行四边形有____   __个；
平行四边形第四个顶点的坐标是              .

如图，已知□ABCD中，点M是BC的中点，且AM=6，BC=12，CD=4，则该平行四边形的面积为             .