八月，天多热。鸡热得_____着翅膀，狗热得_____舌头，蝉热得_____如何是好，在树上不停地_____着“知了，知了”。槐乡的孩子可不怕热，他们背着水葫芦，带着干粮，没等云雀开口歌唱黎明，就已经爬到小山上去了。男孩常常是爬到树上，用长长的钩刀到一下又一下地削着槐米。一簇簇槐米落下来了。女孩有的弯腰捡着，两条辫子像蜻蜓的翅膀，上下飞舞着；有的往篮里塞着槐米，头一点一点的，像觅食的小鸭子。当缕缕炊烟从村中升起的时候，孩子们满载而归，田野里飘荡着他们快乐的歌声。

    This is Kate Smith. She is 13 years old. She lives in Guangzhou. She studies in No.10 Middle school. Her parents work there. They are both English teachers. They are form the UK. She likes eating junk food. She doesn't like playing sports. She has one healthy habit: She sleeps for 9 hours every night.
    Kate Smith has a brother. His name is Jack Smith. He is 11 years old. He doesn't eat junk food. He likes playing sports. He often runs, plays basketball, and goes swimming. He eats fruit every day. He likes eating vegetables. But he has an unhealthy habit: He sleeps for 6 hours every night.

向下图试管里的水中加入下述某种物质后，原来U型管内在同一水平上的红墨水，右边液面降低了些，左边液面上升了些，则加入的物质是      （    ）