user: Question: What is the position of the player who is from the United States and has 30 minutes? 
Columns: ['Name', 'Nationality', 'Position', 'Appearances', 'Starts', 'Minutes', 'Goals']
Types: ['text', 'text', 'text', 'real', 'real', 'real', 'real']
Sample row: ['Lori Chalupny Category:Articles with hCards', 'United States', 'MF', 1.0, 1.0, 90.0, 0.0]
SQL:

assistant: SELECT "Position" FROM "Table" WHERE "Nationality" = 'United States' AND "Minutes" = 30.0;