I think the correct answer is 'None of the above'. Somalia probably is the right answer here, with Somali being the 'official' language and the others being 'imports'. In the other countries there are so many regional dialects that it takes a National language, such as Swahili or English, for the people to understand each other.
Kenya: English (official), Swahili (national), and several other languages spoken by 25 ethnic groups
Somalia: Somali (official), Arabic, English, Italian
Uganda: English (official), Swahili, Luganda, Ateso, Luo
Zimbabwe: English (official), Ndebele, Shona (85%)