If Africa were to be nuked, what can they do about it?

Let's say all the nuclear superpowers of the world for some reason wanted to turn Africa into a radioactive parking lot. What would Africans be able to do retaliate? Would they even know what hit them? There isn't an African country with a missile defense system or any form of fully competent air force. Life would go on as normal and peaceful for the countries that decided to nuke Africa, while all the people in African countries have been effectively wiped out.