四级作文的写作可以分为以下几个步骤：

1. 确定题目和主题

仔细阅读题目，明确要求。

确定主题，思考可能的论点。

2. 列提纲

根据题目要求，列出至少3个主要论点。

每个论点下可以列出1-2个支持论据。

3. 开头段

引言：简短介绍主题，引起读者兴趣。

表明立场：明确提出你的观点。

4. 主体段

每段围绕一个论点展开。

首句为主题句，概括本段内容。

支持论据：用事实、例子或数据来支持你的观点。

转折或对比：如果需要，可以在此处加入转折或对比，使文章更有层次。

5. 结尾段

总结全文：重申你的观点。

提出建议或展望：如果题目要求，可以在此处提出。

6. 修改润色

检查语法、拼写和标点符号。

确保文章结构清晰，逻辑严密。

以下是一个四级作文的示例：

Title: The Importance of Environmental Protection

Introduction:

With the rapid development of society, environmental problems have become increasingly serious. The importance of environmental protection has been widely recognized.

Body:

Firstly, environmental protection is crucial for the sustainable development of our planet. The depletion of natural resources and the pollution of the environment have led to a series of ecological crises. If we do not take effective measures to protect the environment, our planet may become uninhabitable.

Secondly, environmental protection is essential for the health of human beings. Air and water pollution can cause various diseases, such as cancer and respiratory diseases. Moreover, the destruction of natural habitats can lead to the extinction of many species, which may disrupt the balance of ecosystems and affect human health.

Conclusion:

In conclusion, environmental protection is of great importance. We should take immediate action to protect our environment, such as reducing carbon emissions, conserving water and energy, and planting more trees. Only in this way can we ensure a healthy and sustainable future for ourselves and our descendants.

注意：这只是一个示例，实际写作时请根据题目要求和个人观点进行调整。