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: OBJECTIVE : A multicenter , controlled trial showed that early blockade of the renin - angiotensin system in patients with type 1 diabetes and normoalbuminuria did not retard the progression of nephropathy , suggesting that other mechanism ( s ) are involved in the pathogenesis of early diabetic nephropathy ( diabetic nephropathy ) .
### Output Text:
OBJECTIVE : A multicenter , controlled trial showed that early blockade of the renin - <span class="chemical">angiotensin</span> system in patients with type 1 diabetes and normoalbuminuria did not retard the progression of nephropathy , suggesting that other mechanism ( s ) are involved in the pathogenesis of early diabetic nephropathy ( diabetic nephropathy ) . 