The D double prime layer is considered related to which part?

Correct answer: Near base of lower mantle and core boundary

The direct answer is A: the D double-prime layer lies near the base of the lower mantle, close to the mantle–core boundary. In studies of Earth’s interior, D″ is a deep zone just above the outer core. It is not a separate surface layer like the crust, ocean or atmosphere. The reasoning is: Earth has the crust, mantle and core; the lower mantle reaches down to the core; D″ refers to the unusual region at the bottom of that lower mantle; therefore it is located near the mantle–core boundary. Option A is correct. Option B is wrong because the upper crust is shallow, while D″ is extremely deep. Option C is wrong because the ocean surface is external. Option D is wrong because the atmosphere is far above the solid Earth. Memory cue: the double-prime symbol points to the deep bottom of the mantle, just above the core.