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: At the end of each 14 - day treatment , a dose - response curve ( DRC ) was performed , and airway ( FEV1 , FEF25 - 75 ) chronotropic ( HR ) , tremor , and metabolic ( K , Glu ) responses were measured at each step ( from 100 to 4 , 000 micrograms ) .
### Output Text:
At the end of each 14 - day treatment , a dose - response curve ( DRC ) was performed , and airway ( FEV1 , FEF25 - 75 ) chronotropic ( HR ) , tremor , and metabolic ( <span class="chemical">K</span> , <span class="chemical">Glu</span> ) responses were measured at each step ( from 100 to 4 , 000 micrograms ) . 