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17. Which letter should replace the question mark?
  IQ test. Fast and free online iq test # 4 with answers and solutions. Question # 17. Which letter should replace the question mark?
 

Explanation:
Two sequences of letters alternate: ZXWVTS (Consonant letters in reverse alphabetical order) and AEIOUY (Vowels in alphabetical order). Both sequences are written clockwise. The letter Y is sometimes considered a sixth vowel because it can sound like other vowels.