- when there is a math problem.
- when there is a syntax problem.
- when there is a proposal in the offing, and a problem has first been identified.
- when you're talking about a homogeneous mixture of two or more substances--i.e., when one is doing chemistry.
These are books you're talking about. BOOKS, the word "solutions"!
Is a movie theater a "cinematic experience solution"? Are shoes "bare feet solutions"? Is a taco a "TexMex deficiency solution"?
The word "solutions," please never behave this way again.
I'm not kidding,