A : What's your favourite invention?

B : Of course computers. They are very important in people's life now.       

A: I like computers, too. I think they will be used even more widely in the future.

B: I agree with you.        

A: I usually use my computer for looking up information reading books and playing games;

B: Do you like shopping online?

A : Yes, of course.       

B: That's true. However, sometimes it isn't safe to buy things online.

A: Yes, so we should be careful when shopping online. What do you like to do with your computer?

B:        

A: You must have many net friends.

B: Sure. I have about 10 friends who are from different countries.

A:        

复数$z=\frac{-3+i}{2+i}$的共轭复数是（   ）

设函数$f\left(x\right)=\left(x^2-6x+c_1\right)\left(x^2-6x+c_2\right)\left(x^2-6x+c_3\right)$，集合M=x|{f（x）=0}={x₁,x₂,x₃,x₄,x₅}⊆N*，设c₁≥c₂≥c₃，则c₁-c₃等于（    ）