能量既不会凭空 ____，也不会凭空 ____，它只会从一种形式 ____为其他形式，或者从一个物体 ____到另一个物体，而在 ____和 ____的过程中，能量的总量保持 ____，这就是能量守恒定律．

在以“力”为主题的辩论赛中，正方和反方提出了许多观点，小明把他们的观点归纳整理如下表．你认为正确的观点有（　　）

①两个物体相接触，就一定有力的作用；②两个物体相接触，但不一定有力的作用；③力的产生至少涉及两个物体；④一个物体也可以产生力的作用；⑤力的维持物体运动状态的原因；⑥力是改变物体运动状态的原因．

    Keeping a diary in English is one of the best ways to improve our English writing ability.

    Compared with other forms of writing, it is shorter and takes ____(little) time. It can help us to develop the habit of thinking in English.____we stick to this practice,____ (gradual) we'll learn how to express (表达) ourselves in English. In keeping a diary in English, we certainly run up against many ____ (difficult). In the first place, it often ____(happen) that we have trouble ____(find) proper words and phrases to give expression to our mind. And____ is very hard for us to put them into English properly.

    As far as I am____(concern), my suggestion is that we should always have a notebook and a Chinese­English dictionary within easy reach. We can also turn to our English teacher for help, if necessary. In short, I believe that it is ____great use to keep a diary in English for the development of ____ (we) writing skills.