Theoretical approaches can only be said to be, valid. if________?
Athey are shared by a large enough number of theorists
Bthe theorist has researched the literatures thoroughly
Cthey are written in such a way as to be impossible to disprove
Dthey have been tested out by means of factual research
Correct answer
D. they have been tested out by means of factual research
Explanation
The correct answer is they have been tested out by means of factual research.