Why is mortality/attrition not an internal threat to the validity of this study?

Group of answer choices

A. The survey was noninvasive, simple, and easy to understand, making it appealing for participants to complete it

B. Participants had to come back for the survey, giving researchers reason to worry they may not show up

C. Participants were not exposed to traumatic events as part of the research process

d. The survey was taken in one session