Which country of europe experiences the greatest seismic activity, including both earthquakes and volcanic eruptions?

Italy

Explanation:

The European country that experiences the greatest seismic activity is Italy. The seismic activity is manifested through both volcanic eruptions and earthquakes. The reason for this is that Italy is located near the boundary between the Eurasian and African tectonic plates. This boundary is a very complex collision boundary, where there is lot of pressure between the two continental plates, causing constant adjustments in the crust, resulting in constant earthquakes. Also, there are volcanoes, which have emerged on the land. Vesuvius and Etna are actually one of the best known volcanoes in the world, with Etna being one of the most active volcanoes in the world.

a and b because with the other three, they simplify to something else.