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: METHODS : Data were extracted from 2021 paired mother - infant records for the year 2000 birth cohort in New Hampshire ' s 25 delivery hospitals .
### Output Text:
METHODS : Data were extracted from 2021 paired mother - infant records for the year 2000 birth cohort in New Hampshire ' s 25 delivery hospitals . 