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: This observation prompted a Phase I clinical study of lometrexol given with folic acid supplementation which has confirmed that the toxicity of lometrexol can be markedly reduced by folic acid supplementation .
### Output Text:
This observation prompted a Phase I clinical study of <span class="chemical">lometrexol</span> given with <span class="chemical">folic acid</span> supplementation which has confirmed that the toxicity of <span class="chemical">lometrexol</span> can be markedly reduced by <span class="chemical">folic acid</span> supplementation . 