DNA克隆(DNA cloning)

写出一个最大的八位数和最小的六位数，并求出它们和与差．

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。

How to Make Friends

Friendship is a very important human relationship and everyone needs good friends.  Good friendship has many benefits.  It offers companionship, improves self-worth and promotes good health.  There are times in our lives such as when we have recently moved into a new town, or changed our jobs or schools.  Such changes often leaves us without a friend   71 .  But for many of us the process is difficult and requires courage.  Below are some helpful suggestions on how to make and keep friends.

1.  Associate with others.

The first step to making friends is associating with other people.  You can go to public places to meet new people.  Besides, you will need to make yourself known by becoming an active member of such places.

2. Start a conversation

Starting a conversation is the second most important step in making new friends.  72   You can always start the conversation.  Being able to make small talk is a very useful skill in relating with other people. 

3. 73   

Choosing friends with common interests is important in building friendship as these interests would always bring you and your friend together, Hanging out will always be a pleasant experience.

4. Let it grow.

It is a good thing to stay in touch.  However, try not to press your new friend with calls, messages or visits as this would likely wear him or her out and finally you may lose your friend.    74  .  The best friendships are the ones that grow naturally.

5. Enjoy your friendship

The best way to enjoy your friendship is to allow your friends to be themselves.     75   Try not to change them from who they are to what you want them to be.  Become the kind of friend you will want your friend to be to you.

A． Be cheerful.

B． Do things together.

C． Do not wait to be spoken to.

D． Try not to find fault with your friends.E.  Making new friends comes easy for some people.

F.  For a friendship to develop you need to stay in touch.

G.  So you will need to give your friend time to react to you.

有机磷杀虫药中毒主要死因为循环衰竭。（）

物业管理法律关系的构成要素，包括（）。

A．主体

B．当事人

C．客体

D．内容

隧道工程易发生的伤害有哪些？