20. Fill in the circles in the figure below with 0 and 9, using each number only once, so that the sum of the numbers on each line segment is 13.



Translate the above text into English, please keep the line breaks and format of the source text, and output the translation result directly.
【Analysis】As shown in the figure, $a-h$ are counted 3 times, $x$ is counted 4 times, and $y$ is counted 2 times. 
Thus, $10 \times 13=3 \times(0+1+2+\cdots+9)+x-y \Rightarrow y-x=5$
Since $a+g+b=c+x+y=h+e+d=13 \Rightarrow f=6$
Therefore, $c+d=a+h=b+x=7 \Rightarrow f=6$
Thus, $a, b, c, d, x, h$ are $0, 2, 3, 4, 5, 7$ respectively
So, $e, g, y$ are $1, 8, 9$ respectively
Also, $y-x=5$, so $y=8$ or 9
If $y=8$, then $x=3 \Rightarrow b=4 \Rightarrow e=1 \Rightarrow g=9 \Rightarrow a=0 \Rightarrow d=10$ which is a contradiction
Therefore,
$$
\begin{array}{l}
y=9 \Rightarrow x=4 \Rightarrow b=3 \Rightarrow e=1 \Rightarrow g=8 \\
\Rightarrow a=2 \Rightarrow d=7 \Rightarrow c=0 \Rightarrow h=5
\end{array}
$$