力的三要素是力的大小、方向和____ ．

初中生小B是个铁杆“追星族”，可在学习上却不肯用功。自从进入初中以来，他的数学成绩就没有及格过。老师多次给予教诲，他却说：“我崇拜的那些大歌星上学时的数学成绩还没我现在的好呢。”
对于小B如此的追“星”行为，你的忠告是什么？ 

    Good habits are important to us. We should build good living habits. Now let's have a look at the two brothers. Li Qiang and Li Gang are brothers. But their living habits are different. Now let's go to Li Qiang's room. Li Qiang cleans his bedroom every day and puts his things away. Look! There is a computer on the desk. There are two balls under the bed. A guitar and a kite are on the wall. Some books are on the shelf. So he must be a careful boy. Now let's go to Li Gang's room. The room is not clean. Can we see his clothes on the desk? Oh, yes. We can see a football and a knife on the desk, too. Li Gang never does any cleaning on weekends. So his room is in a mess.

    What do you think of Li Qiang and Li Gang? Li Qiang is a good boy. Li Gang must learn from his brother

【提出问题】金属与盐酸反应剧烈程度受哪些因素的影响？

【做出猜想】a.可能与金属本身的性质有关；b.可能与盐酸的浓度有关。

【设计探究】实验所用金属均已用砂纸打磨。