已知函数f(x)=|x²-2ax+b| $\left(x\in R\right)$，给出下列命题：
（1）f(x)必是偶函数；
（2）当f(0)=f(2)时，f(x)的图象关于直线x=1对称；
（3）若a²-b$\le$0，则f(x)在区间a,$+\infty$)上是增函数；
（4）f(x)有最大值|a²-b|.
其中正确的命题序号是（     ）

    A little girl grew a 40-pound cabbage, feeding 275 people. Now, she's 1it her life.

    Most children have2such as playing outside and swimming with friends. But this little girl has a hobby that's3from all of her friends. And it was this hobby that has4her to be able to help her community.

    5Katie Stagliano was around 9 years old, she was given a class project to 6her first cabbage in her home garden. It didn't even take long to7and begin to grow. As friends came over, they pointed out it is8than any of theirs. They asked her what she had 9and she just told them that she watered it every day. But it didn't 10long for it to grow bigger and bigger. It grew so large that the cabbage11weighing 40 pounds! Kate then decided that she could use this cabbage to do something12for the community. So she took the huge cabbage to a local soup kitchen, where they13 it with ham and rice. Because of her cabbage, 275 poor people were14

    She began to realize that15and helping people are what she likes to do most. So, she decided to16her first garden on the land.

    Katie is now 18 years old, and has set up her own non-profit organization called “Katie's Krops” with the17of her family friends. She has 18over 200,000 dollars! And there're over 100 “Katie's Krops” in the US. She   19gardening and loves encouraging other children to experience the20of gardening as well.

一名宇航员在某星球上完成自由落体运动实验，让一个质量为2kg的小球从一定的高度自由下落，测得在第5s内的位移是18m，则（    ）