This was a little tricky. The clue is in the question. It is telling you to read every third spot... literally. So the third spot in every word is as follows:
Read - a
Every - e
Third - i
Spot - o
Young - u
a-e-i-o-u - All vowels. Sometimes "y" is a vowel and the third letter in Psycho is a "y" making that the correct answer. There is no other commonality or conclusion that could be drawn from the other choices.