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: All six patients had supersaturated bile ( mean ( SEM ) cholesterol saturation index of 1 . 19 ( 0 . 08 ) ( range 1 . 01 - 1 . 53 ) ) and all had abnormally rapid cholesterol microcrystal nucleation times ( < 4 days ( range 1 - 4 ) ) , whilst in four , the bile contained cholesterol microcrystals immediately after sampling .
### Output Text:
All six patients had supersaturated bile ( mean ( SEM ) <span class="chemical">cholesterol</span> saturation index of 1 . 19 ( 0 . 08 ) ( range 1 . 01 - 1 . 53 ) ) and all had abnormally rapid <span class="chemical">cholesterol</span> microcrystal nucleation times ( < 4 days ( range 1 - 4 ) ) , whilst in four , the bile contained <span class="chemical">cholesterol</span> microcrystals immediately after sampling . 