According to the Textbook, Why Did an "Affirmation Intervention" Help

According to the textbook, why did an "affirmation intervention" help to improve the grades of minority students?

A) The self-affirmation helped to block the worries prompted by stereotype threat, and therefore stereotype threat did not reduce student's performance.
B) The self-affirmation helped to change students' theories of intelligence from entity to incremental.
C) The self-affirmation helped to reduce the biases the students held against doing well in school.
D) The self-affirmation helped to improve teachers' perceptions of the students.