根据意思写出相应的词语

①原形容水势广大的样子。后形容事物的广阔壮大，或前进的人流声势浩大。____ 

②比喻像乌龟的头缩在甲壳一样藏起来 ____ 

    One terribly cold day, a snowstorm hit our area. Needing firewood, I quickly set out with my best friend, Bruce, to look for a tree to cut down. Cutting down a tree in a snowstorm can be dangerous. ① So to have a friend who could warn me of dangerso was important.
    When I chose a big 23-meter-tall tree and prepared to cut it down, Bruce suddenly warned me, “Don't cut down that tree! It's too close to the power line!” I wasn't sure about it. So I decided to disregard his warning. I couldn't wait to finish the job and go back home. I began cutting down the tree.② When the tree fell, there was no longer any doubt whether my friend was right.
    The tree caught the power line, bringing it to the ground. I considered cutting the tree off the line. After all, electricity can't travel through wood. As I reached out my finger to touch the tree, pain ran up my arm and through my head. I had been shocked!
    After I returned home and told my mother what happened, she quickly called the power company. Workers from the power company soon arrived. One of them asked if I had touched the tree, and when I told him I had, his face turned pale. “You should have been killed,” he said. It was my boots that saved my life.
    ③Within two hours, the workers removed the tree. Soon the snowstorm calmed down——but not my mother. Even though she was glad that I wasn't hurt, my mother was still serious with me. After all（毕竟）, I shouldn't have brushed off my friend's warning.

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（     ）

如图，物体的重力是20 N，请画出物体所受力的示意图；

— What did the teacher say just now?

— Sorry. I didn't catch it. I ________ about something else.