The numbers from $1$ to $40$ are written on $40$ pieces of paper, respectively, and put into a box. A piece of paper is chosen at random. Find the probability of choosing a number greater than $20$. 
选项为:A:$$\frac{1}{2}$$  B:$$\frac{1}{3}$$  C:$$\frac{1}{4}$$  D:$$\frac{2}{5}$$  请回答其中一个选项.