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: They were given a ten day pretreatment with either L - alpha - GFC or placebo , p . o . , and on the eleventh day either scopolamine or placebo , i . m .
### Output Text:
They were given a ten day pretreatment with either <span class="chemical">L - alpha - GFC</span> or placebo , p . o . , and on the eleventh day either <span class="chemical">scopolamine</span> or placebo , i . m . 