问题 单项选择题

正整数N可以被3整除。()
(1)N是4个连续正整数之和,其中第1个可以被3整除
(2)N是5个连续正整数之和,其中首尾两个都不可以被3整除

A.条件(1)充分,但条件(2)不充分。

B.条件(2)充分,但条件(1)不充分。

C.条件(1)和(2)单独都不充分,但条件(1)和条件(2)联合起来充分。

D.条件(1)充分,条件(2)也充分。

E.条件(1)和(2)单独都不充分,条件(1)和条件(2)联合起来也不充分。

答案

参考答案:D

解析:

由条件(1),设第一个数为3k,则此时N=3k+3k+1+3k+2+3k+3=12k+6=3(4k+2),即显示Ⅳ是可以被3整除的,即(1)充分;由条件(2),首尾两个都不可以被3整除的5个连续正整数之和即为N=3k+1+3k+2+3k+3+3k+4+3k+5=15k+15=3(5k+5),可以被3整除,(2)充分。

阅读理解

What do you think of a forest, what do you see? Just trees? Or do you see many other things, such as singing birds, colorful plants and wild flowers?

The forest is a whole of its own. It is full of many different living things. But even though they are all different, they have one thing in common: they all need each other in order to live on.

The trees feed the forest "people" by making food in their leaves; by using sunlight to join water and minerals from the soil and air. Their deep network of roots joins the soil together and stops it from dying out, making it possible for living things to live in it.

Human beings are like the living things in the forest. We need one another in order to live. We need the farmers to grow our food, railroad and truck drivers to bring it to our shops and clerks (售员)to sell it to us. We need people to prepare our food and cook it and others to take our waste things away. Then, of course, we need doctors, nurses, government leaders, mailmen, telephone operators, and many others.

We also need other human beings in another way. We need people for friendship, to talk over our problems, exchange ideas. Think how lonely and unhappy you would be if you lived all alone.

Life is a matter of giving and taking. We need to help other people as much as we need other people to help us. Think what a good feeling you have when you have done something for someone else. You know, being a volunteer is so great!

小题1:According to the text, colorful plants and flowers live on______.

A.the leaves of the trees

B.water and minerals

C.the soil and air

D.all of the above小题2:It is the ________ that make it possible for living things to live in the forest.

A.birds

B.trees

C.plants

D.farmers小题3:According to the writer, human beings are_______the forest "people".

A.like

B.dislike

C.unhappy with

D.different from小题4:The writer mainly wants to tell us ________.

A.we need people for friendship

B.the forest is a whole world of its own

C.we need one another in order to live on

D.the forest is full of different living things小题5:Which one is the relationship (关系) between a forest and your life?

A.We are trees in the forests.

B.We like the living things in the forest.

C.We need farmers to grow our food in the forest.

D.We are the same as the forest: we need each other to live on.

单项选择题