D. Tick (✓) the correct simple machine. 1. Staircase 2. Curtain strings 3. Tip of the drilling machine 4. Knife blade 5. Steering wheel 6. Long rod used to move a big rock 7. Door knob 8. Light bulb Wheel and Axle/Inclined Plane Wedge/Pulley Lever/Screw Wedge/Wheel and Axle Lever/Wheel and Axle Inclined Plane/Lever Inclined Plane/Wheel and Axle Lever/Screw​