Question

which statement best describes the theory of plate tectonics?
plates sometimes move closer to one another.
sections of earth that shift are part of earth’s asthenosphere.
sections of earth’s continents are in slow, constant movement.
parts of the ocean floor move as they are carried by rift valleys.

Explanation:

1. Analyze Option 1: Plates sometimes moving closer (convergent boundaries) is part of plate tectonics, but it's a partial description.
2. Analyze Option 2: Tectonic plates are part of the lithosphere (crust and upper mantle), not the asthenosphere (semi - molten layer below lithosphere), so this is incorrect.
3. Analyze Option 3: The theory of plate tectonics states that the Earth's lithosphere is divided into plates (which include continental and oceanic crust) that move slowly and constantly due to convection currents in the mantle. This option accurately describes the core idea of plate tectonics regarding the movement of continental (and oceanic) sections.
4. Analyze Option 4: Ocean floor movement is related to seafloor spreading at mid - ocean ridges, not being carried by rift valleys (rift valleys are formed by divergent boundaries on land or at mid - ocean ridges, but the description of ocean floor movement being "carried by rift valleys" is inaccurate).

Answer:

C. Sections of Earth’s continents are in slow, constant movement.