user: Question: Which class had a number under 4 and was built in 1988?
Columns: ['Class', 'Type', 'Built', 'Number', 'Withdrawn']
Types: ['text', 'text', 'text', 'real', 'real']
Sample row: ['Class 170 Turbostar', 'diesel multiple unit', '1999–2004', 4.0, 2005.0]
SQL:

assistant: SELECT "Class" FROM "Table" WHERE "Number" < 4.0 AND "Built" = '1988';