【简答题】牙膏是和牙刷一起用于清洁牙齿,保护口腔卫生,对人体安全的一种日用必需品.某研究性学习小组对某一品牌牙膏中所含摩擦剂的成分及含量进行了如下探究. 【查阅资料】 (1)牙膏常用氢氧化铝、碳酸钙、二氧化硅等物质作摩擦剂,牙膏中其它成分遇到盐酸时无气体生成; (2)氢氧化铝是两性氢氧化物,在常温下它既能与强酸,又能与强碱反应.如与氢氧化钠可发生如下反应:Al(OH) 3 +NaOH=NaAlO 2 +2H...
【单选题】What is the main idea of the text?
A.
Music has a power to catch all our attention.
B.
Art of high values can improve us as human beings.
C.
It's difficult to express our satisfaction from works of art.
D.
Simple entertainment is easy to understand and can give us pleasure.
【多选题】N三3 很大的榴莲切开分为小份装盘出售就是( )。
【判断题】When Shepard left school in 1961, he began his training in writing plays.