The disadvantages are that you have to pay for them, they have a steep learning curve, and they don't allow you access to their source code in case you need to modify a feature.

而缺点是您需要为它们付费，有一段陡峭的学习曲线，而且当您需要修改功能时不允许您访问源代码。

youdao

For the majority of folk, reading or learning a current skill has become the focus of their lives and the source of their happiness and contentment afterward their retirement.

对大多数人来讲，退休以后，阅读或壆习一项新技术已成为他们生活的中心和快乐的来源。

youdao

For the majority of people, reading or learning a new skill has become the focus of their lives and the source of their happiness and contentment.

对于很多人来说，学习一门新技术占据了他们的生活和充实了他们的生活。美。

youdao

Edutools compares open source and proprietary learning content management systems in terms of their features.

UNESCO: Free and Open Source Software for E-learning