In Convectional Current Theory rising and descending currents together form what?

Correct answer: Convection cycle

Direct answer: Option A, convection cycle. In convection theory, heating creates density differences. Warmer, less-dense material rises, while cooler, denser material descends. These two opposite movements are not separate unrelated events; together they complete a repeating circulation. That repeating circulation is called a convection cycle or convection cell. Option A is therefore correct. Option B, river delta, forms where a river deposits sediment, usually near its mouth; it is not produced by rising and sinking currents. Option C, glacial lake, is formed by ice-related erosion or melting and has no connection with this mechanism. Option D, desert dune, is a wind-shaped deposit of sand, not a heat-driven internal circulation. The reasoning is: heat causes rising, cooling causes sinking, and the two movements together make a cycle. Exam cue: rising plus descending material equals convection cycle.