关于物态变化的探究．

如图是一物质发生物态变化时，温度与时间的变化曲线．

阅读下面短文，根据短文内容回答问题

Dear Wang Fang,

    Thank you for your letter. You wrote to ask me about American social customs(风俗) in their dinner party. You are asking the right person. I once lived in America for five years. Now I'll tell you something about it.

    It's a good idea to bring a small present when you go to a dinner party. Flowers are always nice, or you may bring a bottle of wine if you know that your friends drink it.

    You should arrive(到达) on time or five minutes late. Don't get there early. If you're going to be more than fifteen minutes late, you should call before.

    Try to be free at the dinner table. If you don't know about choosing(选择) the right fork or knife, just watch the other people, and follow them. If you still have no idea of what to do, ask the person beside you .

    If you like the food, say so. Of course, you'll thank them for the meal and for their kindness. It's also a good idea to send a card to thank them the day after.

Rose

Answer the following questions with No More Than 5 Words

晓丽发现妈妈经常忘记关掉厨房的窗户、水龙头、煤气开关、电磁炉开关．为消除安全隐患，她想设计如下电路：

在厨房门口安装红、黄两只灯泡．当煤气、电磁炉没有都关闭时红灯亮，都关闭时红灯灭；当窗户、水龙头没有都关闭时黄灯亮，都关闭时黄灯灭．

现在，给你红、黄两只灯泡，一个定值电阻，4个开关，电源和导线若干，请你帮他在图中画出这个电路图.（元件画在相应虚线框内）．

给下面的字选择正确的读音。

bēi   biē    xì    jì

我收拾好背____包，把它系____在筏子上。

如图所示，细绳长为L，吊一个质量为m的铁球（可视为质点），球离地面的高度h=2L，绳所能承受的最大拉力为1.5mg，绳的上端系一质量不计的环，环套在光滑水平杆上，现让环与球一起以速度v= $\sqrt{gL}$ 向右运动，在A处环被挡住而立即停止，A离墙的水平距离也为L，求：