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: Glomerular filtration rate ( GFR ) and effective renal plasma flow ( ERPF ) were measured by inulin and para - aminohippurate ( PAH ) clearance , respectively .
### Output Text:
Glomerular filtration rate ( GFR ) and effective renal plasma flow ( ERPF ) were measured by inulin and <span class="chemical">para - aminohippurate</span> ( <span class="chemical">PAH</span> ) clearance , respectively . 