Which keyword are indicative of statements of fact?

a. i believe; i know; i think; i affirm
b. witness; observe; discover
c. confirmed by; reported by; understood
d. research says; verified by; experts state

D.research says; verified by; experts state

Of the possible responses, only Option D is indicative of statements of fact because to have a statement attributed to research and experts in the field or to have been stated by an expert indicates that there is no opinion or analysis on the write’s behalf as only facts are being stated.  All other options indicate a belief, an interpretation/analysis, and an understanding.  

The key words that are indicative of statemens of fact are research says; verified by; experts state. Option D is correct.

A fact is defined as a statement that is true and can be either proven or verified objectively. To put it simply, a fact is true and correct. This words show that a stament is a fact since those words do not convey an opinion; they may present certain information which was proven by experts who researched and are really sure of what they are saying, so that their information is accurate.

the correct answer is the first one.