Question:
Who was the chair of United States Senate Committee on the District of Columbia in May, 1821?

Context:
 Robert Henry Goldsborough is the chair of United States Senate Committee on the District of Columbia from Jan, 1817 to Jan, 1819. 
 James Barbour is the chair of United States Senate Committee on the District of Columbia from Jan, 1821 to Jan, 1823. 
 Armistead Thomson Mason is the chair of United States Senate Committee on the District of Columbia from Jan, 1816 to Jan, 1817.

Answer:
Question:
Who was the chair of United States Senate Committee on the District of Columbia in May, 1821?

Context:
 Robert Henry Goldsborough is the chair of United States Senate Committee on the District of Columbia from Jan, 1817 to Jan, 1819. 
 James Barbour is the chair of United States Senate Committee on the District of Columbia from Jan, 1821 to Jan, 1823. 
 Armistead Thomson Mason is the chair of United States Senate Committee on the District of Columbia from Jan, 1816 to Jan, 1817.

Answer:
user
James Barbour
assistant
Question:
Who was the chair of United States Senate Committee on the District of Columbia in May, 1821?

Context:
 Robert Henry Goldsborough is the chair of United States Senate Committee on the District of Columbia from Jan, 1817 to Jan, 1819. 
 James Barbour is the chair of United States Senate Committee on the District of Columbia from Jan, 1821 to Jan, 1823. 
 Armistead Thomson Mason is the chair of United States Senate Committee on the District of Columbia from Jan, 1816 to Jan, 1817.

Answer:
user
Robert Henry Goldsborough
Armistead Thomson Mason
assistant
Question:
Who was the chair of United States Senate Committee on the District of Columbia in May, 1821?

Context:
 Robert Henry Goldsborough is the chair of United States Senate Committee on the District of Columbia from Jan, 1817 to Jan, 1819. 
 James Barbour is the chair of United States Senate Committee on the District of Columbia from Jan, 1821 to Jan, 1823. 
 Armistead Thomson Mason is the chair of United States Senate Committee on the District of Columbia from Jan, 1816 to Jan, 1817.

Answer:
user
James Barbour
assistant