Which of the following represents a fundamental structural difference in how a two-stroke engine and a four-stroke engine handle the intake and exhaust processes?

1. Two-stroke engines use ports in the cylinder wall opened and closed by the piston, while four-stroke engines use valves in the cylinder head operated by a camshaft.
2. Two-stroke engines use a camshaft in the crankcase to open exhaust valves, while four-stroke engines do not have a camshaft.
3. Two-stroke engines require a turbocharger to intake air, while four-stroke engines rely on gravity.
4. Two-stroke engines have valves that open twice as fast as the valves in a four-stroke engine.