Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Compression zones is the opposite of rarefaction zones, where air molecules in waves are loosely packed.
What is the opposite of rarefaction zones, where air molecules in waves are loosely packed?

Sodium chloride is an odorless white solid that is harmless unless consumed in large quantities.
What is an odorless white solid that is harmless unless consumed in large quantities?

Poetically speaking, nature reserves are islands of what, in a sea of habitat degraded by human activity?
Poetically speaking, nature reserves are islands of what, in a sea of habitat degraded by human activity?