 Complete the following phrase:  1994 also saw the reintroduction of refuelling during the race for the first time since . After Sennas fatal crash at Imola, several rule changes were introduced to slow the cars. In Spain, front wing endplates and rear diffusers were reduced in size. For the following race in Canada, the effectiveness of the airbox was reduced by means of holes cut into the engine cover, resulting in less power. From Germany onwards, a 10 mm wooden plank was affixed to the underside of every car to reduce ground effect advantages, whilst also forcing an increase in ride height. Wear was permitted on the plank up to 1 mm by the end of the race. After winning in 