user: Question: What was the guage of the concessionaire Ferrosur Roca?
Columns: ['Concessionaire', 'FA Division(s)', 'Gauge', 'Length, km', 'Takeover Date']
Types: ['text', 'text', 'text', 'real', 'text']
Sample row: ['Ferroexpreso Pampeano', 'Roca, Sarmiento, Mitre', 'broad', 5094.0, '1 Nov. 1991']
SQL:

assistant: SELECT "Gauge" FROM "Table" WHERE "Concessionaire" = 'Ferrosur Roca';