Table 1 shows the Human Development Index (HDI) value for Mauritius over the period 2015 to 2019.
| Year | 2015 | 2016 | 2017 | 2018 | 2019 |
|---|---|---|---|---|---|
| Mauritius HDI Value | 0.789 | 0.793 | 0.797 | 0.801 | 0.804 |
All other things being equal, which one of the following is most likely to explain the trend shown in Table 1?
A decrease in the Gini coefficient of income distribution
An increase in gross national income (GNI) per capita measured at purchasing power parity (PPP)
A reduction in the country's carbon dioxide (CO2\text{CO}_2CO2) emissions per capita
An appreciation of the Mauritian rupee exchange rate against the US dollar