Which of the Following Is NOT One of the Weaknesses

Which of the following is NOT one of the weaknesses of the research studies supporting Reading Recovery?

A) Attrition in these studies was very high.
B) Teachers who administered Reading Recovery had more training than teachers in the control group.
C) Reading Recovery shows less efficacy when used with children who have reading problems.
D) Reading Recovery shows less efficacy when used with ethnic minority children who have reading problems.