Two brothers worked together on a farm.  One was married and had a large1. The other had no wife yet. Although they lived in different houses, they shared everything they got from their farm.
    One day, the single brother said to himself, "It's not2that we share all the rice. I'm3and I need less than my brother. " So, every night he took a bag of rice from his store-room and4across the field 5their houses, putting it into his brother's store-room.
     At the same time, the married brother thought, "It's not fair to share all the rice. I’m married and I have my wife and children to6me when I am7. However, my brother has no one to take care of his8 " So, each night he also took a bag of rice and put it into his brother's store-room.
    Several months passed by. They found9strange that their rice never became less. Then, one dark night the two brothers ran into each other. Slowly they began to understand what was happening. Their bags fell onto the ground and tears10 their eyes at once.

血液在血管中的流向是（    ）

我们知道方程2x+3y=12有无数个解，但在实际生活中我们往往只需求出其正整数解．

例：由 $\{\begin{array}{c}\frac{x}{60}+\frac{y}{30}=6.5\\ \frac{x}{50}+\frac{y}{40}=6\end{array}$ ，得： $\{\begin{array}{c}x=150\\ y=120\end{array}4$ （x、y为正整数）．要使y=4﹣ $\frac{2}{3}$  x为正整数，则 $\frac{2}{3}$  x为正整数，由2，3互质，可知：x为3的倍数，从而x=3，代入y=4﹣ $\frac{2}{3}$  x=2．所以2x+3y=12的正整数解为 $\{\begin{array}{c}x=3\\ y=2\end{array}$ 问题：