Which of the Following Is a Challenge for Understanding How

Which of the following is a challenge for understanding how media shapes our attitudes?

A) Researchers rely on surveys and people are rarely interested in completing surveys about media.
B) Researchers rely on people's self-reports of what media they have watched, which could be inaccurate.
C) The studies often have poor internal validity.
D) Researchers rely on measures that are difficult for people to understand.