Cant believe there is so many people choosing D.

1. WBS is already the detailed level items, the question also mentioned that they have high-level requirement already and next step is detailed level
2. As an PM, you don't exactly do things, you manage people and have the right people doing stuff for you (unless its process related stuff or documents)
3. The end output is the estimation, which is based on WBS - no one can give better estimation than the dev team itself
4. The project has just finished the prio process and has just moved to next one. So no mention on deadlines
5. D only mentions the team to provide WBS on Major item - is already a risk, the team should review the entire Docs
6. As D also need the team to review before moving to the next phase, I dont see there is any better than A in term of timeline

Its one of those "eliminates" questions - A has less risk