Related Clues:

• ''Horton Hears a __!'' (Seuss book)
• '___ knows?'
• Time-traveling Doctor
• You-know-__
• First word of 'Blowin' in the Wind'
• First of the five W's
• '___ dat?'
• 'Explain'
• Trainee's question
• Major medical grp
• Start of many a 'Jeopardy!' response
• '___ knew?'
• Doctor of British sci-fi
• First baseman, to Abbott and Costello
• By which means