Read the passage. Answer the question that follows. Iceland is prone to frequent earthquake shocks and volcanic eruptions. From careful records that have been preserved, we learn that since the beginning of the twelfth century, Iceland has practically not gone longer than 40 years without having an earthquake or volcano. These volcanic eruptions are often very lengthy; one eruption lasted six years. During a volcanic eruption in Iceland, the ground is split into fissures or cracks, generally parallel to each other, and varying in width from a few inches to several yards. Which sentence states the central idea of the passage? Records of earthquakes go back to the 12th century. Iceland has some volcanos, but they are not a threat. Fissures and cracks are common markers of a volcanic eruption. Iceland has a long and frequent history of volcanic eruptions.