All information concerning official borders was taken from the following website:https://www.cia.gov/library/publications/the-world-factbook/geos/za.html

1- The only way to go from South Africa to Uganda by crossing only 2 countries is to go through Mozambique and Tanzania :

A2 = Mozambique, A3 = Tanzania

2- The only country adjacent to both Namibia and South Africa is Botswana B1 = Botswana

3- The 3 countries adjacent to both Botswana and Mozambique are South Africa (A1), Zambia (150m official border in Kazungula) and Zimbabwe. B2 is bordering B3 and C2, whereas Zimbabwe has only one remaining neighbour not already in the quiz (Zambia), so B2 can’t be Zimbabwe

B2 = Zambia

4- The only remaining country that borders both Zambia and Namibia is Angola C2 = Angola

5- The only remaining countries adjacent to both Zambia and Tanzania are Malawi and DRC. B3 must also border B4 and C3, so as all the neighbours of Malawi are already in the quiz, B3 can’t be Malawi

B3 = Democratic Republic of Congo

6- The only remaining country to border both Angola and DRC is Republic of Congo (adjacent to Cabinda, exclave province of Angola)

C3 = Republic of Congo

7- The only countries bordering both DRC and Uganda are South Sudan and Rwanda. However, Rwanda is not a valid possibility as it has only one remaining neighbour not in the quiz (Burundi) whereas B4 is still adjacent to B5 and C4

B4 = South Sudan

8- The only remaining country bordering both South Sudan and the Republic of Congo is the Central African Republic

C4 = Central African Republic

9- The only remaining countries that border Uganda are Rwanda and Kenya. Once again, Rwanda is not a valid possibility because of having only one remaining bordering country not already in the quiz (Burundi)

A5 = Kenya

10- The only remaining country bordering Kenya and South Sudan is Ethiopia B5 = Ethiopia

11- The only remaining country bordering Ethiopia and Central African Republic is Sudan C5 = Sudan

12- The only remaining country bordering Kenya is Somalia A6 = Somalia

13- The only remaining country bordering Somalia and Ethiopia is Djibouti B6 = Djibouti

14- The only remaining country bordering Djibouti and Sudan is Eritrea C6 = Eritrea