肾气丸主治中小便证候，既可是小便______，又可表现为小便______。

若函数y=log_a（3-ax） 在[0，1]上是减函数，则a 的取值范围是______．

将用¹⁵N标记的一个DNA分子放在含有¹⁴N的培养基中复制n次，则后代中含¹⁵N的单链占全部DNA单链的比例和含有¹⁵N的DNA分子占全部DNA分子的比例依次是[ ]

A．1/2ⁿ，1/2ⁿ

B．1/2ⁿ，1/2^n-1

C．1/2ⁿ，1/2ⁿ⁺¹

D．1/2^n-1，1/2ⁿ

体内不易分解的气体或易挥发性毒物主要为（）

A.经呼吸道排出

B.经肾排出

C.经肠道排出

D.经皮肤排出

E.随眼泪排出

阅读理解。

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。选项中有两项为多余选项。

     Facebook (a social networking service) makes it far too easy to make new friends-Unfortunately, reality

is not like that.   1   The difference here is that we don't get to choose our families; friends, on the other hand,

are picked, selected and developed through our life.

     It is quite funny how your best friends know exactly what your are thinking without even telling them.

   2   This friend's sixth sense is something that takes time to develop through many long-lasting experiences

that your go through.

     I was once asked: which one would be the worst thing, to lose all your loved ones or to lose all your

friends?   3   I believe that I couldn't live a day if I had lost all my friends.

      Respect, loyalty (忠诚), and support are few of the qualities that will form a good friendship. There are

many others for sure, but it is enough for you to get these. 

       4   The ability to trust someone and therefore, be trusted, can be only built with a lot of effort and time.

     I hate that ugly Facebook's message "Add to your friends?" It is like a friends was something that you

could simply add to your "portfolio (文件夹)" without feeling.   5   

A. My answer was certainly the latter.

B. This is definitely not the way to make friends.

C. This is not something that happens overnight.

D. Life without friends is just like soup without salt.

E. We need friends to help us when we meet with difficulties.

F. Trust is also one of the major features of a good relationship.

G. Friends sometimes are just as important to us as our families.

下列生态系统中生物种类较少、群落结构单一，在人的作用消失后会很快消失的是( )。

A．草原生态系统
B．淡水生态系统
C．农田生态系统
D．森林生态系统