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: Primary tumor sites were oropharynx , 10 patients ; hypopharynx , four ; larynx , two ; oral cavity , three ; unknown primary , two ; and nasal cavity and parotid gland , one each .
### Output Text:
Primary tumor sites were oropharynx , 10 patients ; hypopharynx , four ; larynx , two ; oral cavity , three ; unknown primary , two ; and nasal cavity and parotid gland , one each . 