Why C? And why not the others?

Correct answer: C. The Ring of Fire

The Ring of Fire is a horseshoe-shaped belt of oceanic trenches and volcanic arcs that partly encircles the Pacific basin, running from South America up through Central America, North America, across to Russia and Japan, and down through Southeast Asia to New Zealand; USGS attributes about 90% of the world's earthquakes and most of its active volcanoes to this single zone, where the Pacific Plate grinds against its many neighbors. The Alpide Belt is the genuine second-place seismic zone, running from Java through the Himalayas to the Mediterranean, and it is a real near-miss since it accounts for a meaningful share of the planet's largest earthquakes, just far less than the Pacific belt. The Andean Volcanic Belt is a real and significant chain of volcanoes, but it is only the South American segment of the larger encircling belt, not the whole ring itself. The mid-ocean ridge system is an enormous undersea mountain chain in its own right, but it marks where plates pull apart rather than where they collide, so it is not the earthquake-and-volcano belt described here.

Source: USGS: 'This Dynamic Earth' (pubs.usgs.gov/gip/dynamic/fire.html)