The correct answer is - C. Basque.
In using the linguistics as a parameter for grouping the people in Europe in large basic ethnic groups, there's four major groups, the Slavic, Germanic, Latin, and Finno-Ugric.
The Slavic being the biggest group, both by territory, and by population, than come the Germanic and the Latin that dominate the western half o Europe, and the smallest of the four is the Finno-Ugric group.
The biggest three are all groups that share a common ancestor, both ethnically, and linguistically, they belong to the Indo-European family. The Finno-Ugric group, on the other side, belongs to a totally different group of people, and to a totally different language family.