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: Children on both studies had significant attention problems , but P9605 children scored below average on more neurocognitive measures than those treated on P9201 ( 82 % , 14 / 17 measures vs . 24 % , 4 / 17 measures ) .
### Output Text:
Children on both studies had significant attention problems , but P9605 children scored below average on more neurocognitive measures than those treated on P9201 ( 82 % , 14 / 17 measures vs . 24 % , 4 / 17 measures ) . 