It can be seen from the graph that great changes have taken place in the number of training classes in the past fifteen years. On the one hand, before the 90s, the increase of the training classes was not so great. On the other hand, there has been a sharp increase in the training classes after the 90s.

What are the reasons for the change? There are three reasons for this. First, with the development of the society, more and more people pay much attention to the improvement of their ability, which they hope to improve through special training classes. Second, to most people, training plays a direct part in helping them to attain their goal quickly and efficiently. Third, with the improvement of the people's living standards, more and more people regard it as a preferable way to spend their spare time.

As far as I am concerned, I think it is necessary to attend training classes. For one thing, they can play a very important role in help you to attain your goal quickly and efficiently. For another, you can learn not only what you need quickly but also a new way to broaden your horizon.