Subject: Can you help?            

From: Rose

Dear Knowledgeable,

    I have a good friend, Ann. She is very clever and can speak English really well. A very important English speech contest for our whole city will be held next month. Our classmates all think Ann is the best person to represent the class in the school contest and make sure she will win. But the problem is that she's very shy and that she's terrified of speaking in front of other people.

    She can't tell others about it, because she doesn't want to let her friends down. I can't think of any good advice to give her, but you always come up with good solutions to people's problems. Can you give us some good advice？Do you think we can tell the truth to the rest of the students?

Yours,

Rose

夏天，被蚊子叮咬之处常会出现肿胀、瘙痒等症状，这是人体对蚊子毒素其主要成分为二 甲基亚硝胺(CH₃)₂N₂O的过敏引起的。

(1)二甲基亚硝胺是由____  种元素组成的；

(2)科学家实测出蚊子口器刺入皮肤的平均刺入力为1．65×I0^-6牛，这么小的力能刺穿皮肤是因为减少____ 而增大了作用效果。

在中国市场上10瓶水中有7瓶是纯净水。可是这种常见的瓶装水却引发了中德科学家的争议。部分德国专家认为，纯净水非但不含矿物元素，而且还会带走体内的矿物元素，隐含健康风险。而中国的科学家则认为，纯净水中的矿物元素并不重要，纯净水也是安全的。对于一些尚未定论的事物，我们要有科学争论的勇气，更要有勇于实践的胆识、善纳争论的胸怀。一种观点、理论或者一项决议遭到公开的争论并不是多么可怕的事情，相反是促进科学进步、决策合理、社会和谐的突破口。

为什么我们要有科学争论的勇气，更要有勇于实践的胆识？