Please help me!!

Review the main idea.
The workforce for Egyptian pyramids was highly specialized.

Which detail best supports the main idea?

(A) The construction of the pyramids was a huge accomplishment

(B) Experts today estimate that 20,000 - 30,000 laborers worked on the pyramid at one time.

(C) Whichever space ramp was used, Egyptian workers toiled extremely hard.

(D) It was divided into groups that had specific tasks: raising a wall, building the roof of a burial chamber, and so on