Explanation:

In the terminology used in United Nations statistics, the "Sub-Saharan region" typically includes areas of Africa that are south of the Sahara Desert. Considering the listed regions:

Sahel: it is included in some definitions of "Sub-Saharan Africa."

Sahara region: This is not included in Sub-Saharan Africa, as it is the northern boundary.

Horn of Africa: Generally considered part of Sub-Saharan Africa.

Kalahari region: Located in southern Africa, definitely part of Sub-Saharan Africa.

Hence, regions 1,3 and 4 (Horn of Africa and Kalahari region) are  included in the “Sub-Saharan region” as per United Nations terminology.