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: BACKGROUND / AIMS : Recently ribavirin has been found to inhibit angiogenesis and a number of angiogenesis inhibitors such as sunitinib and sorafenib have been found to cause acute hemolysis .
### Output Text:
BACKGROUND / AIMS : Recently <span class="chemical">ribavirin</span> has been found to inhibit angiogenesis and a number of angiogenesis inhibitors such as <span class="chemical">sunitinib</span> and <span class="chemical">sorafenib</span> have been found to cause acute hemolysis . 