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: Diarrhea , flatulence , abdominal pain , and weight loss were common for combination recipients . ( ABSTRACT TRUNCATED AT 250 WORDS )
### Output Text:
Diarrhea , flatulence , abdominal pain , and weight loss were common for combination recipients . ( ABSTRACT TRUNCATED AT 250 WORDS ) 