In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: RESULTS : The average platelet counts preoperatively , and on POD 7 , 14 , and 21 were 65 , 88 , 149 , and 169 x 10 ( 9 ) / L , respectively .
### Output Text:
RESULTS : The average platelet counts preoperatively , and on POD 7 , 14 , and 21 were 65 , 88 , 149 , and 169 x 10 ( 9 ) / L , respectively . 