1021
Four of these five subjects also performed mixed sequences under conditional control of the words ( e . g . , A1 - - - - B2 - - - - A3 - - - - B4 - - - - A5 and its reversal ) , verifying that the stimuli which occupied the same position in each sequence were members of the same class .
 None
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 None