The correct answer is (d). Sudan is not part of the Horn of Africa. The Horn of Africa is a peninsula in East Africa that juts out into the Red Sea and the Gulf of Aden. It is bordered by the Arabian Peninsula to the northeast, the Gulf of Aden to the east, the Indian Ocean to the southeast, the Somali Sea to the south, and the Gulf of Tadjoura and Djibouti to the west. The countries that are part of the Horn of Africa are Djibouti, Eritrea, Ethiopia, and Somalia.
Sudan is a country in northeastern Africa. It is bordered by Egypt to the north, Libya to the northeast, Chad to the west, the Central African Republic to the southwest, South Sudan to the south, Ethiopia to the east, and Eritrea to the northeast. Sudan is the largest country in Africa by area, and the third-largest in Africa by population.