The correct answer is (A) To confuse; to bewilder; to mislead; to perplex; to mix up. Also, to disorder; to contradict or refute; to defeat.

Confound comes from Old French confondre, Latin confundere (mingle, mix).

Examples of use:

• What happened during the following week confounded his vacation plans.
• The directions that accompanied his son's Christmas toy confounded him.