The research we discussed on problem solving suggests that

A$.$

Just proivde the answer to a similar question $($without asking them to solve the problem$)$ will best prepare students to answer the eventual test question.

B$.$

Having students engage in trying to solve a problem $($problem oriented instruction$)$ will help them to sovle the problem later.

C$.$

Just present the list of answers for the students to memorize is boring but the most effective way to help them prepare for the test.

D$.$

These are all equally effective.