Which Approach Appears to Be Most Effective for Teaching English

Which approach appears to be most effective for teaching English speakers a second language?

A) Let them talk with native speakers of the language, who should alternate between using English and the other language.
B) Teach it to them before kindergarten if possible, because they quickly lose their ability to learn a second language fluently after that.
C) Immerse them in the second language, having them hear and speak it exclusively in all classroom activities.
D) Wait until they reach Piaget's formal operations stage so that they can better grasp the subtleties of the new language.