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: Nine patients ( 37 % ) developed acute grade II - IV GVHD , and 11 of 17 evaluable patients ( 64 % ) developed chronic extensive GVHD .
### Output Text:
Nine patients ( 37 % ) developed acute grade II - IV GVHD , and 11 of 17 evaluable patients ( 64 % ) developed chronic extensive GVHD . 