Final answer:
Nursing theories and research provide a foundation for evidence-based nursing practice that defines the rationale for nursing actions.
Step-by-step explanation:
In nursing, theories and research provide a foundation for evidence-based nursing practice. The correct answer to the question is a) Evidence. Nursing theories help define the rationale for nursing actions by utilizing evidence from research. Evidence-based practice in nursing involves using the best available evidence, integrating it with clinical expertise, and considering the patient's preferences and values to make informed decisions about patient care.