Book excerpt: You always said you were smart. Now here's a chance to prove it, with the most challenging crossword collection ever. There are very few black squares in these crosswords, which means that most of the answers are long. Some of the information required challenges every facet of your general knowledge. And even when the answers aren't hard, the clues can be quite tricky. Try this, in the long answer category: what's a 15-letter word for Psychiatrists' suggestions, sometimes? In the area of specialised learning, do you know what Limon or Vanila (10 letters) refers to? And in the matter of tricky clues: what's the five-letter answer to 'nui loa' ('Fondest regards, ' in Maui)? Give up? Answers: ANTIDEPRESSANTS, BACARDI RUM, and ALOHA. If you can fill in all the blanks in these 72 cranium crushers, you're super smart, indeed. About MENSA: - Mensa is the internationally renowned high IQ society which has a worldwide membership of almost 100,000 members in more than 100 countries. There are 28,000 members in the UK, including 2,200 Junior Mensans under the age of 16.To join Mensa, the only requirement for membership is that an individual's IQ falls within the top 2 per cent of the populatio