What is the answer?

You are developing your IT development project team. Some of the team members need training on the latest software that you are using. Which of the following documents will be the most help in finding out the information about the scheduled training for the team members?

A. Project Staff Assignments

B. Training Management Plan

C. Staffing Management Plan

D. Human Resource Management Plan

I chose C, because according PMBOK training needs are documented in Staffing Management Plan. But the answer accroding to the author is D.

Please help clarify this.

Question source: PMexam simulator. 

I Would say C as well, and that's according to the PMBOK