求电视机箱所占空间的大小就是求电视机箱的（  ）

同体积、同物质的量浓度的BaCl₂溶液可分别使同体积的Fe₂(SO₄)₃、ZnSO₄、K₂SO₄三种溶液中的SO₄^2-完全沉淀，则三种硫酸盐中金属离子物质的量浓度之比为

已知函数$f\left(x\right)=\ln x-\frac{1}{x}$，若函数f（x）的零点所在的区间为（k，k+1）（k∈Z），则k=____ 

认真阅读课文第二，四自然段，找出最能概括该自然段意思的句子，抄下来。

第二自然段：____

第四自然段：____

    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.