如图，是边长为25cm的活动四边形衣帽架，它应用了四边形的____ ．

如图是电源电压恒为220V的电热烘干箱的基本电路图，S是双掷开关，R₁是发热电阻，定值电阻R₂为110Ω，当S接“2”时，R₁的电功率是110W，试求：

根据短文理解，从A、B、C、D四个选项中选择最佳一项填空。

    Learning how to play the piano is not the only way for children to have a bright future. Children can choose what they like in many ways. Many children are good at sports. Maybe they will be great players when they grow up.

    Here is another example: the 1 in Shanghai have paid much attention to story-telling. Story-telling can also make them 2 excellent students. They 3 many story-telling contests every year. And children have 4 great interest and taken an active part in them. Some students who were too shy to speak in public have been now very good 5. 

    Now many parents 6 their children to learn how to play the piano or the violin. 7 the money and energy they spend cannot make sure that their children will 8 much in a short period of time. However, training children to tell a story is quite9.Although it costs little, it's a good and an easy way 10 children to develop.