Why are there two types of endoplasmic reticulum?

Hi there,

The two types of endoplasmic reticulum is the rough endoplasmic reticulum (rough ER) and smooth endoplasmic reticulum (smooth ER)

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i think the answer is b.

the sun's light combined with the visible wavelenghts form what is called ultraviolet radiation, which are the long waves at the end of a visible light sprectrum.

hope it ,

bioteacher101