Table: expansion_draft_players
Columns: pos
nationality
previous_team
nba_years_a
career_with_the_franchise_b

Question: What is the previous team of the United States player who had 2 NBA years and played the F position?
SQL: SELECT "previous_team" FROM expansion_draft_players WHERE "nationality" = 'united states' AND "nba_years_a" = 2 AND "pos" = 'f'