Final answer:
The British empiricists and continental rational philosophers set the stage for the philosophical movement of Existentialism.
Step-by-step explanation:
The subject referred to in this question is Philosophy. The British empiricists and continental rational philosophers set the stage for various philosophical movements. In this case, the theories and ideas of these philosophers laid the foundation for the development of Existentialism, a philosophical movement emphasizing individual existence, freedom, and choice. Therefore, the correct answer is A. Existentialism.