Which evidence best supports this claim?

The school district should remove "free" or "study" periods from the school schedule in order to make the school day more efficient.

A. Many parents of our students are unaware that their children have one or more free periods each day during which they can catch up on work.

B. Research shows that little actual schoolwork gets done in study periods and that midday breaks actually lower knowledge retention rates.

C. A poll of 100 teachers in our district revealed that the new homework limits have boosted standardized test scores considerably.

D. Youth behavioral expert Lenore Cook notes that the mental separation and stress relief of study halls are key to a student's ability to focus in the classroom.