Why Is It Important to Conduct a Usability Test with a Team

Why is it important to conduct a usability test with a team as opposed to a single usability specialist?

A) Usability testing involves a lot of work.
B) Usability testing involves watching for small details that are revealed very quickly during testing.
C) A well-rounded team can develop more effective test materials than a single person can.
D) All responses are correct.