According to Your Authors, Which of the Following Would Promote

According to your authors, which of the following would promote the BEST growth of cognitive skills?

A) Once a child masters basic addition, move right to subtraction.
B) Once a child masters basic addition, move to slightly more difficult addition problems.
C) Once a child masters basic addition, move to multiplication so the child can see that multiplication is really just advanced addition.
D) Once a child masters basic addition, keep the child at that level for at least a few days so that the skills have time for consolidation.