What is the preferred mode of decay for nuclei that are neutron-rich? for nuclei that are neutron-poor?

• A. Neutron-rich nuclei: positron emission
  Neutron-poor nuclei: beta emission or electron capture
• B. Neutron-rich nuclei: alpha decay
  Neutron-poor nuclei: gamma emission
• C. Neutron-rich nuclei: alpha or beta decay
  Neutron-poor nuclei: positron or neutron emission
• D. Neutron-rich nuclei: neutron emission or beta decay
  Neutron-poor nuclei: positron emission or electron capture

Answer: (D)