21.   In part it was the intellectual challenge, but it was also allegiance to an early mentor.

22.   Laboratory denizens are usually perceived as motivated by purely intellectual challenges, not money-grubbing impulses.

23.   More important, the show is so full of visual revelations and intellectual challenges that the revolutionary nature of its collective spirit is clear.

24.   Moreover, she has found that while the day is regimented, there is a wider range of intellectual challenges.

25.   Rather, she said, they appeared to write viruses for the intellectual challenge or to relieve boredom.

26.   Schmidt clearly relishes the intellectual challenge of the task.

27.   The appeal of virus-hunting, he explains, is the fast pace, the satisfaction of craftsmanship and the intellectual challenge.

28.   The biggest intellectual challenge is trying to keep track of the cast.

29.   The essence of a successful novel to Johnson is intellectual challenge, to the writer himself and his readers.

30.   The search for the perfect spot is, for him, an intellectual challenge, a point of pride, a personal quest.