初中语文第四册第三单元属于科技说明文单元。这一单元所选课文 ,有的阐明某一现象的科学原理 ,有的阐释某一领域的科学观点。《食物从何处来》(以下简称《食》)作为本单元的首篇课文 ,很好地体现了“例子”作用。我们试想 ,自然界的生物品种繁多 ,千姿百态 ,生活环境和条件各? The third unit of the fourth grade of the junior high school language belongs to the science and technology exposition unit. The texts selected in this unit shed light on the scientific principles of a phenomenon, and some interpret the scientific viewpoints of a certain field. The first article of this unit, “Where Food Comes From” (hereinafter referred to as “Eat”) is a good example of the role of “examples.” Let us imagine that there are many kinds of creatures in the natural world, in various forms, and in terms of living environment and conditions.