Which of these statements about an oil drilling rig is not true?

1. Through the drill pipes, at the extremity of which the drill bit rotates, a special mud is injected which the mud engineer prepares and controls. This mud cools the drill bit and consolidates the sides of the borehole to avoid a gushing of oil gas or water from the layer being drilled.
2. The cuttings fragments of rock crushed by the drill bit are brought back up to the surface by lifting the drill bit and extracting core samples from the hollow tube.
3. The most usual tool is an assembly of three cones made of very hard steel which crushes the rock.
4. The derrick is the visible part of the drilling rig. It is a metal tower several tens of meters high used to vertically introduce the drill strings down the hole.
5. Drill strings are made up of metallic tubes screwed end-to-end. They transmit a rotating movement called "rotary drilling" to the drilling tool.
6. Core samples brought up to the surface reveal the thickness of the layers and the nature of the rock.