在一个晴朗的天气里，小颖在向正北方向走路时，发现自己的身影向左偏，你知道小颖当时所处的时间是（　　）

已知（如图2）：（I）NaClO₂饱和溶液在温度低于38℃时析出的晶体是NaClO₃•3H₂O，高于38℃时析出晶体是NaClO₂；（Ⅱ）30% H₂O₂超过40℃时会完全分解；（Ⅲ）高于60℃时NaClO₂分解成NaClO₃和NaCl．

．如下图所示，试管中盛有某种液体，将气球中的某种固体小心的倒入试管中，不能观察到气球变大的一组物质是   

阅读短文，选择合适的答案。

    I study at Yu Hong Primary School in Guangzhou. I have forty-seven classmates (同学). Twenty-three are boys and twenty-four are girls. Our classroom is a nice one. It's very big. There are four windows and two doors in it. We have a big blackboard and a small one. The big one is for our teachers and the small one is for us. Mr. Li is our Chinese teacher. He is an old man. We don't like him at all. But Miss Chen, our English teacher, is a young woman. She is very nice. We all like her very much. So we like English the best. We often play basketball with Miss Chen.

化简分式（x－y+$\frac{4xy}{x-y}$）（x+y－$\frac{4xy}{x+y}$）的结果为   （       ）