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: Grade less than or equal to 2 nausea and vomiting occurred in 66 % courses and phlebitis in the infusion arm in 37 % .
### Output Text:
Grade less than or equal to 2 nausea and vomiting occurred in 66 % courses and phlebitis in the infusion arm in 37 % . 