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: After a 30 - min baseline measure of locomotor activity ( day 0 ) , animals were maintained on a cyclic diet of 12 - h deprivation followed by 12 - h access to 10 % sucrose solution and chow pellets ( 12 h access starting 4 h after onset of the dark period ) for 21 days .
### Output Text:
After a 30 - min baseline measure of locomotor activity ( day 0 ) , animals were maintained on a cyclic diet of 12 - h deprivation followed by 12 - h access to 10 % <span class="chemical">sucrose</span> solution and chow pellets ( 12 h access starting 4 h after onset of the dark period ) for 21 days . 