阅读下面短文，然后从所给的四个选项中选出一个最佳答案。
Learn English speaking FREE with TalkEnglish.com. Our goal is to help you learn English speaking so you can speak English fluently. Improve your spoken English free!
Steps to learn English.
To become a fluent English speaker, you must study and master reading, listening, and speaking. At TalkEnglish.com, the lessons are structured(打造) to give you practice in all three areas at the same time.
Reading Step 1: Identify
Speaking English Fluency Step 2: Understand
Listening Step 3: Integrate
A complete and effective solution to Learn English speaking.
TalkEnglish.com developed the "Click, Listen, and Repeat" functionality(功能). In most of the lessons, you read the sentence, click on the sentence to listen to the sentence, and then you can practice speaking by repeating after the audio file(音频文件) provided by a native English speaker. This method improves your reading, speaking, and listening all at the same time and makes learning English easy. You will improve your English speaking using this method.
nC（气）；△H=Q（n为正整数）在不同条件下反应混合物中C的百分含量和反应过程所需时间的关系曲线。