The correct answer is - b. High-latitude.
The climate zones that are marked on this map with the number 4, are climates zones that are occupying the high-latitude areas. The subarctic, tundra, and highland climates, are characterized with very cold climates, the year is dominated by winter. They usually don't have high precipitation, but are bellow average, or even dry.
In general, this climate zones are not considered as suitable for living for the humans, and that is the reason why this areas are having very few people living in them.