What’s porosity?
The options are down below

answer:

Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure the "accessible void", the total amount of void space accessible from the surface.

b.

developed countries have tended to improve the environment, while developing countries have tended to damage it.

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