Which one of the following is not a member country of the Mano River Union?

The Mano River Union (MRU) is an international association initially established between Liberia and Sierra Leone by the 3 October 1971 Mano River Declaration.It is named for the Mano River which begins in the Guinea highlands and forms a border between Liberia and Sierra Leone. On 25 October 1980, Guinea joined the union.

The goal of the Union was to "accelerate the economic growth, social progress and cultural advancement of our two countries ... by active collaboration and mutual assistance in matters of common interest in economic, social, technical, scientific and administrative fields".