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: The leading causes of death were pneumonia and bronchitis ( 44 . 1 % ) , malignant neoplasms ( 11 . 6 % ) , heart diseases ( 4 . 1 % ) , cerebral infarction ( 3 . 7 % ) and septicaemia ( 3 . 3 % ) .
### Output Text:
The leading causes of death were pneumonia and bronchitis ( 44 . 1 % ) , malignant neoplasms ( 11 . 6 % ) , heart diseases ( 4 . 1 % ) , cerebral infarction ( 3 . 7 % ) and septicaemia ( 3 . 3 % ) . 