Based on the Human Development Index (HDI), a country is typically considered highly developed if its HDI is 0.90 or above.
In the given options:
- Country A: 0.91 (Highly developed)
- Country B: 0.64 (Not highly developed)
- Country C: 0.39 (Not highly developed)
- Country D: 0.75 (Not highly developed)
Therefore, Country A (0.91) can be considered highly developed based on the HDI.