Based on the Human Development Index (HDI), a score of 0.91 indicates a highly developed country. Therefore, Country A with an HDI of 0.91 can be considered highly developed.
The other countries have lower HDI scores:
- Country B: 0.64 (medium human development)
- Country D: 0.75 (medium human development)
- Country C: 0.39 (low human development)