如下图，用边长为a的正方形制作的七巧板拼成一只小猫，则小猫头部（图中阴影部分）的面积是____ ．（用a的代数式表示）．

氨气____硫化钠____氢氧化钠____二氧化碳____氮气____次氯酸____．

中国古代四大名著之一的      被美国NBC电视台改编并取名为《The Monkey King》(猴王)。文中空格处应填写  (    )

阅读下面短文，在空白处填入一个适当的词，或填入括号中所给单词的正确形式。

    In recent years,sandstorms ____(occur) in China frequently,especially in northwestern areas, ____severe influence has caused wide concern in China.

There're several reasons for this.First of all,people are cutting down trees without planting more, ____(make) some land become deserts.Another reason is ____it rains less due to the environment pollution.

    To ____(efficient) prevent sandstorms,first,we should plant more trees and grass which can keep the soil ____ being washed away.Second,more green fences should ____(build) along the desert, ____it helps to control the process of the desertification.

    Let's take action to do what we can ____(prevent) sandstorms from today.Soon the golden days we have been looking forward to ____(come).