In the sentence extracted from biomedical literature, identify all the disease entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="disease"> to denote a disease.

### Input Text: The relative risk ( RR ) of CHD was 1 .
### Output Text:
The relative risk ( RR ) of <span class="disease">CHD</span> was 1 . 