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: RESULTS : No reaction was observed with placebo and eight patients ( 88 . 8 % ) tolerated CE .
### Output Text:
RESULTS : No reaction was observed with placebo and eight patients ( 88 . 8 % ) tolerated <span class="chemical">CE</span> . 