At What Point Does an Incomplete or Problem Respondent Constitute

At what point does an incomplete or problem respondent constitute an acceptable respondent that the researcher will allow into data analysis?

A) This is up to the researcher. A researcher must have a definition or otherwise specify the criteria for an "acceptable respondent."
B) An incomplete or problem respondent doesn't ever constitute an acceptable respondent. All of the answers have to be completed.
C) When at least 75% of the answers have been completed
D) When there are no demographic questions left to answer
E) When all but the screening questions have been answered