平日沉默寡言的岳阳同学在今天的数学课上提出一个新颖的解题方法，老师和同学们不由自主地为她鼓掌，她感受到了别人对自己的认可和欣赏。自此以后，她的发言越来越踊跃，性格越来越阳光。这表明（    ）

①自尊和被人尊重都是快乐的     ②她陷入了虚荣的误区

③自信是成功的基石                     ④告别自卑就能走向成功

冬天人们用嘴往手上呵气，手会感到暖和，是利用____ 方法改变手的内能；用双手互搓，同样可使手变得暖和，这又是利用____ 方法改变手的内能．

行列式$\left|\begin{array}{cc}\cos 20°& \sin 40°\\ \sin 20°& \cos 40°\end{array}\right|$的值是____ 

短文改错

假定英语课上老师要求同桌之间交换修改作文，请你修改你同桌写的以下作文。文中共有10处错误，每句中最多有两处。错误涉及一个单词的增加、删除或修改。

增加：在缺词处加一个漏字符号(Λ)，并在其下面写出该加的词。

删除：把多余的词用斜线(＼)划掉。

修改：在错的词下划一横线，并在该词下面写出修改后的词。

注意：

1）每处错误及其修改均仅限一词；

2）只允许修改10处，多者(从第11处起)不计分。

My brother used to ask me question whenever he did his homework, that made me annoyed. But every time he accepted my explanations I feel that I was the smartest person in the world. Answered his questions, I always liked to say that he was so stupid to solve such simple problems.

Last week both of them got the report cards from our school. Unexpectedly, I got a lot of Bs, though he got As. To make things worse, all that day my brother screamed how foolish it was for me not to ask questions! I could say nothing but admit that he was right. I have never made a fun of him since then.

气孔分布下表皮比上表皮多，这样既能保证气体交换又可防止阳光直接照射引起水分的过度散失．