人类使用电能的过程就是把电能转化为其它形式能的过程，如人们利用日光灯，主要是为了把电能转化为（   ）

已知三角形两边长分别为2和9，第三边的长为二次方程x²-14x+48=0的一根，则这个三角形的周长为(   )

我国的外流河，绝大数多数流入（    ）

    Today is Sunday. My Brother and I1at home. We2to take two boxes to the room.3box is big, but it's light(轻）. My brother's box is4, but heavy（重）. We put5on the table. We can see6clothes in the boxes, but my7aren't in them. I8find my socks. My Brother can9me to find them. They're10the bed. And my shoes are under it, too. I must look after (照看)my things. We put the11boxes away. The chair is12. My Brother and I can mend(修理)it. After that, we13basketball14the playground(操场). We are very happy. We like this15.

如图为生态系统碳元素的循环途径（图中数字表示过程），请回答下列问题：