15212
Forty 2 ' - O , 4 ' - C - methylene bridged / locked nucleic acid ( 2 ' , 4 ' - BNA / LNA ) aptamers were isolated from an enriched pool and classified into six groups according to their sequence .
 Chemical: methylene
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: methylene