如图, 与
交于点 O ,
, E 为
延长线上一点,过点 E 作
,交
的延长线于点 F .
( 1 )求证 ;
( 2 )若 ,求
的长.

比较大小: ______
.
宏观辨识和微观探析是化学学科核心素养之一。我国科学家利用复合光催化剂人工合成了燃料,反应的微观示意图如下。下列说法错误的是
A . 丙是较为清洁的燃料
B . 反应后氧元素的化合价升高
C . 一个乙分子中含有 10 个电子
D . 参加反应的甲和生成丁的质量之比为 11 : 8
如图选项中能正确描述平面镜成像特点图是( )
A .
B .
C .
D .
On a hot day, many people like to go to the beach. Some beaches, however, are not safe for swimming.
At some beaches, there are sharks in the water. So people put out shark nets. They help stop too many sharks from getting close to the beach. Sharks can still swim under or around the net. But if they try to swim through, they will get caught. Sharks can die if they are not cut free.
Shark nets don’t just catch sharks. They can catch other animals, too. They have caught dolphins, stingrays and turtles. Even a whale has been caught in a shark net. I took many people to get it free.
Some animals are not so lucky. They are killed in the nets. One day, a whale was swimming with her calf. The calf got caught in a shark net. The mother whale tried to get the calf to come with her. The calf was caught in the net. It couldn’t get free. The mother had to watch it die.
Many people think shark nets should not be used. Sharks are important to the ocean. They eat sick and dead fish. They help to keep the ocean clean. Sharks are the lions and the tigers of the sea.
Some people think there are other ways to keep beach safe for people. Sharks potters are people who watch for sharks. They go to a high place. Then they can look down on the beach. If they see a shark, a siren (汽笛) will sound. They put up a white flag. Then people get out of the water.
After all, the water is a shark’s home.
1 . What can we know about shark nets according to the passage?
A . They are used to keep sharks from coming near the beach.
B . People place them to catch sharks, dolphins, stingrays and turtles.
C . Sharks will be caught when they get close to them.
D . All the animals caught by them are set free.
2 . What does the underlined word “calf” mean in paragraph 4?
A . A huge whale. B . A young whale.
C . A father whale. D . A mother whale.
3 . What does the writer imply (暗示) about the beach safety?
A . People should keep away from beaches.
B . Everyone should work as a shark spotter.
C . It’s not the best way to put out shark nets.
D . Some dangerous beaches should be shut down.
“ 天问一号 ” 火星探测器是中国人民的骄傲,因为它是我国首次登陆火星的探测器。着陆火星的 “ 祝融号 ” ,质量为 ,在牵引力的驱使下,
匀速运动了 100m ,假设祝融号在火星上受到的阻力是其在火星上所受重力的 0.06 倍,已知
,火星表面大气密度是地球表面大气密度的 0.01 倍, g 取
。
求:
( 1 )祝融号所受的阻力;
( 2 )在这段时间内牵引力做的功;
( 3 )同一物体在地球大气中受到的浮力与它在火星大气中受到的浮力之比。
实验是化学研究物质的基本方法。下列实验方案中,可行的是( )
A.除去二氧化碳中混有的一氧化碳:将混合气体点燃
B.除去氧化铜中混有的木炭粉:向固体中通入一氧化碳后加热
C.检验甲烷中是否混有氢气:点燃气体,在火焰上方罩一冷丽干燥的烧杯
D.区分二氧化碳和一氧化碳:将气体分别通入溶有紫色石蕊的水
函数 的定义域为( )
A . B .
C . D .
Ann didn’t know anything about the news ________ Mrs. Brown told her.
A . because B . until C . if
下列反射中,属于人类特有的是
A .青梅入口,分泌唾液 B .谈论青梅,分泌唾液
C .看到青梅,分泌唾液 D .嗅到青梅,分泌唾液
生活中,我们难免会产生紧张、烦躁、焦虑、生气等不良情绪。下列做法不利于情绪调节的是
A.转移注意力或者做放松训练
B.主动寻求父母、老师、同学的帮助
C.把情绪积压在心里,不和任何人说
D.通过运动、唱歌等方式合理地宣泄情绪
Keeping a ________( 日记 ) is a good way to improve our writing skills.
