下列几位同学中，最容易获得真诚友谊的是（    ）

在方格中填上合适的数字是等式成立。

11－3＝____11－4＝____11－5＝____

13－6＝____13－7＝____13－8＝____

15－9＝____15－8＝____15－7＝____

写出复数句。

 Model:  This is an old box.

These are old boxes.

This is a ruler.

____

You probably don't think about soil often, but the following report may help you learn about science of soil.

What is soil made of?

Soil is made of sediments (沉积物) and humus(腐殖质). Sediment is small pieces of rock broken down over time by rain, ice, and wind. Sediment is often found in water. Humus comes from decayed(腐烂的) plants and animals. It helps give plants a lot of the food they need to grow.

How does soil form?

Over centuries, rock breaks down into very small pieces.

The rock pieces mix with humus.

The humus gets thicker and thicker over time. Soil is formed(形成)l

How are soils different?

Soils can be different colors and have different textures(质感). Texture is how the surface of an object feels. Color and texture are two features(特征) of soil.

Plants and soil

Plants do not grow well in some soils. Sandy soi1 is too dry. It does not hold water. Soil with too much clay is too thick. Most plants grow well in dark, rich garden soil that has different sediments and a lot of humus in it.