这篇文章讨论了气候变化的主要问题及其几个子话题，如海平面上升和极端天气事件。

This article discusses the main issues of climate change and several of its ___subtopics, such as sea level rise and extreme weather events.

在数学课程中，代数和几何是主要章节，而概率则是一个重要的子课题。

In the math course, algebra and geometry are main sections, while probability is a key ___subtopic.