在正方体ABCD–A₁B₁C₁D₁中,M,N分别为棱AA₁和B₁B的中点,若θ为直线CM与所成的角,则="    "                                                                                               （   ）                                                

84消毒液是一种以次氯酸钠为主要成分的高效消毒剂．

（1）次氯酸钠溶液呈碱性，原因可用离子方程式表示为　 ____　；

（2）二氧化碳、氢氧化钠、氯化钠三种物质中，添加到84消毒液中可增强其消毒效果的是 ____

（3）84消毒液可以通过电解氯化钠稀溶液制取，电解装置通常选用铁和碳棒为电极，电解时铁电极反应式为 ____

下列化合物中，不是只有C，H，O三种元素构成的是（  ）

下列关于生长素的叙述，正确的是（  ）

阅读理解

    Hello, I'm Jack. I live in a house. My address is 246 Second Street. It's far from the school. So I go to school by bus every day. But my house is near the park. So I often go to the park on foot. Tom is my friend. He lives in a house, too. It is near the school. So he goes to school on foot every day.