What was the biggest shift in thought from Wegener to post-drift studies?

Correct answer: Moving beyond only continents to include ocean floor and mantle processes

Direct answer: Option A, moving beyond only continents to include the ocean floor and mantle processes. Wegener’s continental-drift idea used evidence such as matching continental shapes, fossils, and rocks, but it did not fully explain the mechanism that moved continents. Later post-drift studies added evidence from ocean-floor spreading, ridges, trenches, palaeomagnetism, plate boundaries, and mantle convection. Option A is correct because it describes the major expansion from a mainly continental explanation to a broader Earth-system explanation involving both the surface and interior. Option B is wrong because later research strengthened, rather than completely denied, the idea that large landmasses move. Option C is wrong because Pangaea was a supercontinent, not a river. Option D is wrong because these studies concern Earth structure and movement, not a reduction of geography to weather. Reasoning: continental evidence began the idea; ocean-floor evidence supplied more information; mantle and plate processes provided a wider explanation. Memory cue: Wegener proposed drift; later studies explained the engine and the ocean floor.