美國的官名, 例如 Secretary of State

在 Wiki 的 presidential line of succession (總統不能視事時的繼位名單)
[ http://en.wikipedia.org/wiki/United_States_presidential_line_of_succession#Current_order ]
列出了目前（2008）的候補順序名單如後，
有幾點覺得奇怪：

• 為何 Secretary of the Treasury , Secretary of the Interior 加上定冠詞 the, 其他的Secretary 沒有？
  
• 為何 Secretary of Agriculture, Commerce, Labor 並列, 其他的Secretary卻是分列？
  
• President of the Senate 與 President pro tempore of the Senate 的差別
  

1. Vice President and President of the Senate Dick Cheney
2 Speaker of the House of Representatives Nancy Pelosi
3 President pro tempore of the Senate Robert Byrd
4 Secretary of State Condoleezza Rice
5 Secretary of the Treasury Henry Paulson
6 Secretary of Defense Robert Gates
7 Attorney General Michael Mukasey
8 Secretary of the Interior Dirk Kempthorne
9 Secretary of Agriculture Ed Schafer
— Secretary of Commerce Carlos Gutierrez (non-natural)†
— Secretary of Labor Elaine Chao (non-natural)†
10 Secretary of Health and Human Services Mike Leavitt
11 Secretary of Housing and Urban Development Steve Preston
12 Secretary of Transportation Mary Peters
13 Secretary of Energy Samuel Bodman
14 Secretary of Education Margaret Spellings
15 Secretary of Veterans Affairs James Peake
16 Secretary of Homeland Security Michael Chertoff