Only One of the Teachers Below Is Using a Strategy

Only one of the teachers below is using a strategy consistent with general recommendations regarding the use of homework. Which one?

A) Mr. Trahan gives his students a challenging writing assignment and suggests that they ask their parents to help them with it at home.
B) Mr. Fox sometimes gives students an optional assignment-homework they can do if they want to.
C) Ms. Hewitt counts homework as being worth 50% of students' final grades.
D) Mr. Reichel assigns 20 extra math problems after he learns that his class has misbehaved for a substitute teacher.