我们选择把主体放置在右上交叉点，这样我们可以看到海鸥的整个阴影和指向海鸥的大部分足迹。

We picked the upper-right position for this subject so that we could see the full shadow and most of the tracks that lead to the seagull.

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反应在二重态和四重态势能面上存在四个交叉点，整个反应在二重态势能面和四重态势能面上交替进行。

There exist four cross points in this process on the PES of four and twain states. The reaction conducts in twain and four situation potential energy surfaces alternately.

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