What is the most suitable reason for high heat flow at mid-oceanic ridges?

Correct answer: Hot magma rises and forms new crust there

The direct answer is C, hot magma rises and forms new crust there. A mid-oceanic ridge is a long underwater mountain chain formed where oceanic plates move apart. When the plates separate, hot mantle material or magma rises into the gap. It cools and becomes new oceanic crust, so heat is coming upward from below and the measured heat flow is high. The fact chain is: plates diverge → hot material rises → new crust forms → high heat flow. Option A, higher wind speed, concerns the atmosphere and does not heat the deep ocean floor. Option B, river deposition, occurs where rivers bring sediment, mainly near coasts and deltas, not as the main ridge process. Option C is correct because rising hot magma directly brings internal Earth heat toward the sea floor. Option D, melting glaciers, is a surface climate process and does not explain heat from the oceanic crust. Memory cue: ridge means rising magma, spreading, new crust and high heat.