Propositions are either:

A) sound or valid
B) unsound or invalid
C) true or valid
D) true or false
E) unsound or false

Propositions can be either true or false, and the terms valid and invalid refer to the logical structure of an argument or inference, not individual propositions. A sound argument is one that is both valid (the conclusion follows logically from the premises) and has true premises. An unsound argument is either invalid or has false premises.