user: Question: Which Test Standard has a Usage of Secondary filters, and a Class of F5? Question 4
Columns: ['Usage', 'Class', 'Performance', 'Performance test', 'Particulate size approaching 100% retention', 'Test Standard']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Primary filters', 'G1', '65%', 'Average value', '>5µm', 'BS EN779']
SQL:

assistant: SELECT "Test Standard" FROM "Table" WHERE "Usage" = 'Secondary filters' AND "Class" = 'F5';