Why is it that all the fast-moving fish of the dark current have purple backs and usually purple stripes or spots?

怎么搞的，凡是在深暗的水流中游得很快的鱼都有紫色的背脊，一般还有紫色条纹或斑点？

youdao

His purple wand - which is actually a plastic stake for horseshoes - usually leads, but his body and his whistle work right along with it.

他的紫色棒子- - -实际上是一根马蹄铁塑料桩- - -指挥着，他的身体和哨子很出色地配合着它。

youdao

Beluga usually ranges from purple to black, the palest being the most expensive.

Beluga鱼子酱的颜色一般从紫红色到黑色到有，颜色最淡的的最昂贵。

youdao

Paleontologists usually handle fossils bare-handed, but at the warehouse the scientists were given purple synthetic gloves to wear as they worked.

NEWYORKER: Bones of Contention