 Complete the following phrase:  Pirelli found that 90 of the rear tyres used in free practice for the 2016 Grand Prix had been cut by the bolts securing kerbs to the ground not being drilled into the ground far enough, while Jenson Button and Nico Rosberg expressed concern over the lack of run-off areas which would be dangerous in the case of an incident such as a high speed puncture or mechanical failure. Valtteri Bottas was forced to miss the whole of Free Practice 3 when a drain cover came loose and caused significant damage to his Williams FW38. The first practice session of the 