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？

根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。

    It is important to introduce yourself in a creative, memorable way to distinguish yourself from the crowd. ____ Since being witty(言辞诙谐的) doesn't always come easily, try one of these creative introductions and separate yourself from the rest.

    Write your first or last name on a piece of paper.____ So if your name is Tom, you might say you are tireless, optimistic and mild.

    ____ Then say that you will do so in the words of your“best and worst critic”— your mother. By breaking the ice in this way, you can go on in either a humorous or serious fashion.

    Introduce yourself silently, by drawing a picture of yourself on a large sheet of paper.____  In fact, in some situations, it may be better if you don't. Put a title at the top of your drawing, if you like, such as “Hello! This is me.”

    Turn the traditional introduction upside down by describing yourself in exactly opposite terms of who you are. Have fun with this“back door approach”, and keep people guessing just how much you are exaggerating(夸张).____  Don't bother calling me tomorrow, because I will be hiding in a closet. Send text messages to my girlfriend while I drink a Bud Light on the job.

A. This introduction requires you to be gifted in art.

B. Freely admit that you don't like talking about yourself.

C. It doesn't matter whether you have artistic abilities or not.

D. For example: I am probaby the laziest person you will ever meet.

E. Use each letter as the first letter in an adjective that describes you.

F. Bring in the surprise factor— sometimes known as the shock factor.

G. After all, anybody can stand up and announce their name, business title and job responsibilities.

某有色电解质溶液中，可能大量存在有Ag⁺、H⁺、Cu²⁺、OH^﹣、Cl^﹣离子，你认为：一定没有的离子是____ ，不能确定的离子____ ．

____.