Final answer:
Based on historical practices and the developmental needs of a five-year-old, Nathan would likely advise that Ira should start school, as this is an age-appropriate milestone providing educational and social development benefits.
Step-by-step explanation:
The question pertains to what Nathan advises should happen when Ira turns five years old. While historical context often saw girls getting married at a young age or assisting with family work such as farming, the question likely refers to an educational path or a developmental milestone appropriate for a child of that age. Given this context, the most suitable choice in a modern context, where child welfare and education are prioritized, would be option b) She should start school.