The European challenge for the Breeders' Cup began to look a little clearer when Aidan O'Brien nominated the Mile (gr. IT) as the first preference for Rock Of Gibraltar and the Classic (gr. I) for Hawk Wing.Dual Derby winner High Chapparal is heading for the Turf (gr. IT), following his third place in the Prix de l'Arc de Triomphe (Fr-I), which O'Brien blamed on the lack of a recent prep run.There had been speculation that Rock Of Gibraltar, seeking his eighth group/grade I win in succession, would be tried in the Classic, but O'Brien appears to have ruled that out.However, he said: "As Rock Of Gibraltar and Hawk Wing are entered for two races we had to nominate a preference for each of them, so Rock Of Gibraltar's preferred entry is the Mile, while Hawk Wing's preferred entry is the Classic. But that doesn't mean that the situation cannot change."When the deadline for pre-entries closed on Tuesday, O'Brien had made a total of 10 Breeders' Cup entries, including Landseer in the Mile, and Hold That Tiger, last-gasp winner of the Grand Criterium (Fr-I), Middle Park Stakes (Eng-I) runner-up Tomahawk, Royal Lodge (Eng-II) third Van Nistelrooy, Ontario, and Marino Marini in the Juvenile Colts.Plans for that race will become clearer after Saturday's group I Dewhurst (Eng-I) Stakes at Newmarket.The Breeders' Cup World Thoroughbred Championships is Oct. 26 at Arlington Park.