Haider Is a Master's Student Deciding on His Thesis Topic

Haider is a master's student deciding on his thesis topic. He approaches his advisor and pitches the idea of exploring the use of teacher feedback on subsequent self-confidence. He wants to erroneously tell students they performed poorly on a series of assignments and then examine changes in self-confidence. His advisor is skeptical and asks him to think about ways to tweak the topic. Of the following what is the most likely reason?

A) The study is not ethical.
B) The study is too narrow.
C) The study is not significant.
D) The study is too broad.