Dear editor,

I am a high school student. A few days before, one of my very good friends told me that he was going to stop the school. He said that he want to start his own business. I tried my best to get him change his mind, but failed. I know it is difficult of him to change his mind. He is not doing so good in his studies, yet I want to insist that I give it a try. The process is more important than the results. Now there are only 90 days leaving before the test. I am not sure that his decision is right or wrong. I needed your advice.

自然数中最小的奇数是______，20以内最大的质数是______．