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。
小题1:
If your complaint is immediate, suppose you got the wrong order at a restaurant, make a polite but firm request to see the manager．When the manager comes, ask his or her name．And then state your problem and what you expect to have done about it．
Be polite! 小题2:
But also be firm in making your complaint．
小题3: This doesn’t mean to put on airs and say “do you know who I am?” What it means is that people are often treated the way they expect to be treated．If you act like someone who expects a fair request to be granted, chances are that it will be granted ．
小题4: You are speaking to a voice coming from someone you cannot see．So you can’t tell how the person on the line is reacting．It is easy for that person to give you the run-around.
小题5: If your complaint doesn’t require an immediate response, it often helps to complain by letter．If you have an appliance that doesn’t work, send a letter to the store that sold it．Be business-like and stick to the point．Don’t spend a paragraph on how your uncle John tried to fix the problem and couldn’t．
A．Shouting or acting rude will get you nowhere．
B．Complaining in person or by letter is generally more effective．
C．The worst way to complain is over the telephone．
D．Telephone complaint is never efficient．E．The way to complain is to act business-like and important．
F．Besides, act important．
G．There are many ways to complain．
，则σ2=______．
，求得σ2．由于X1，X2，X3相互独立，所以
相互独立，又EXi=0，
=DXi=σ2．故DY=D(X1X2X3)=E(X1X2X3)2-E2X1X2X3=
-[EX1EX2EX3]2=
，
．