UNC Chapel Hill Statistics 推薦函 - 留學

申請University of North Carolina at Chapel Hill的
STOR department, Statistics PhD program

請問網頁的敘述是總共要恰好三封推薦函，還是最多可到六封呢？

還有就是有沒有一定要相關課程的教授才可以寫推薦函呢？
1. 我碩班是讀電機所，能不能找指導教授寫？修過他的課但沒有統計相關
2. 去中研院做與統計相關的研究，能不能找那邊的研究員寫推薦函？
可是沒有修過他們開的課，因為中研院並沒有開設課程

"Three current letters of recommendation from persons qualified to
evaluate your academic and professional qualifications are required.
You should solicit recommendations from individuals who are familiar
with your academic achievement
and who can address your potential for success in this particular
academic setting. You are allowed to submit a total of six
recommenders in the online system."
http://gradschool.unc.edu/admissions/instructions.html

"Letters of Recommendation 3 -- (from professors of relevant courses)"
http://gradschool.sites.unc.edu/statistics-and-operations-research/

--