The colours are magnificent, but the question of exactly why some trees turn yellow or orange, and others red or purple, is something which has long puzzled scientists.

这些颜色很瑰丽，但究竟为什么有些树会变成黄色或橙色，而有些树会变成红色或紫色，这个问题一直困扰着科学家。

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Some flowers are red, yellow and blue, and others are white.

一些花是红的，一些是黄的，一些是蓝的，其它的是白的。

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What is still not fully understood, however, is why some trees resort to producing red pigments while others don't bother, and simply reveal their orange or yellow hues.

然而，至今仍不完全清楚，为什么有些树木倾向于制造红色素，而有些树木不去刻意制造色素，但还是会呈现出橙色或黄色。

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The horse still shows some of the colors the artist created so long ago: red,black and yellow.

VOA: special.2010.02.03

Some are yellow, some are red, and some are green - does anybody know what this is?

一些是黄色,一些是红色,一些是绿色的,有人知道这是什么吗

耶鲁公开课 - 生物医学工程探索课程节选

They said the temple walls were made of stone and covered in fine yellow clay which also contained some traces of red paint.

BBC: El Paraiso site

"Some schools have a yellow or red card system and I have known members of staff criticised for over-using the red card, " he said.

BBC: Teachers 'too scared to use the red card',

Food in some company cafeterias have been marked red for high-calorie, yellow for medium and green for healthy.

BBC: Taiwan wages nationwide battle with the bulge