（i）过点D任作一条直线与BC边相交于点E₁（如图①），记∠CDE₁=α₁；

（ii）作∠ADE₁的平分线交AB边于点E₂（如图②），记∠ADE₂=α₂；

（iii）作∠CDE₂的平分线交BC边于点E₃（如图③），记∠CDE₃=α₃；

按此作法从操作（2）起重复以上步骤，得到α₁，α₂，…，α_n，…，现有如下结论：①当α₁=10°时，α₂=40°；②2α₄+α₃=90°； ③当α₅=30°时，△CDE₉≌△ADE₁₀；④当α₁=45°时，BE₂= $\sqrt{2}A{E}_2$ ．

其中正确的个数为（   ）

染色体是由____ 和____ 组成的。

阅读短文，然后从方框中选出可以填入文中空白处的单词

teacher   but    old    learn    with    boring     basketball    history    musician

Mr. and Mrs. Cooper are Americans. But now they are in Beijing ____ their kids. This is their first time to China.     

Mr. Cooper is a  ____. He sings very well. Mrs. Cooper is a ____. Her daughter studies at her school. Mrs. Cooper likes Beijing Opera very much. She thinks she can learn about Chinese ____ and culture. So she often goes to see Beijing opera. ____ her daughter doesn’t think so. She likes comedy , and her favorite movie is Mr. Bean. Mr. Cooper doesn’t like movies. He thinks they are____. He likes sports. His favorite sport is ____ . He likes Yao Ming very much. 

The Coopers want to go to Pingyao, Shanxi. It is an ____ and nice place. They want to take photos there. They can also____to speak Chinese. They can have a good time in China.

区里耍举行中学生篮球联赛，九年级(2)班的小龙同学因球技高超，被选人学校篮球队且成为主力。可是本届篮球联赛为期两周，每天下午课余时间还要训

练，这势必耽误中考前的复习。对此，下列认识正确的是(    )

①小龙的个人意愿与集体的共同要求产生了冲突       ②考前复习最重要，小龙应坚决不参加比赛

③小龙的意愿与集体的共同要求是完全对立的           ④小龙应该先参加比赛，再通过找老师、同学补课等方式弥补耽误的时间