It's hard to find a true friend . For most of the time , you may think you can believe（相信）someone , later he may let you down（失望）.

    When you have some difficult times , a true friend will always be there for you . Through good times or____ times , they will try to help you and make you laugh . They will understand you____ you did something wrong . A friend will bring new and exciting things to your life and make your life more interesting .

    True friends will keep your secrets（秘密）and they believe you can also keep____ secrets . When you talk to a true friend , you don't have to worry____ what you may say . You can enjoy this freedom（自由）only with friends .

    However , Friendship is like a two-way street . To find a true friend , you may do the____ thing as your friend does , too . Help your friends when they have problems and share the good things____ them . Give them the same things they give to you . Sometimes friendship breaks very quickly if only one person is giving and trying to keep it .

    There is an old____ , “ Friendship makes the hearts of all the world together ” . You will____ that there is nothing better than having a true friend by your side to share life with .

一个温度是40℃的铁球，吸收2．3×10³J的热量后，温度上升到90℃，求铁球的质量。〔铁的比热容是0．46×10³J/(kg·℃)〕

解析：在公式Q_吸=cm(t－t₀)中，如果已知其中的任意四个物理量，就可以利用方程求出另外的一个，也可以将原公式进行变形，导出一个变型公式，即可求出。

随着年龄的增长，青春期的到来，我们开始关注异性，渴望接触、了解异性，甚至萌发对异性的好感或爱慕之情，你认为下列说法中，正确的是 （    ）

解分式方程$\frac{x-8}{x-7}$−$\frac{1}{7-x}$＝8，可知方程（　　）