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: The drug was given to two groups consisting of castrated and noncastrated rats and compared to two groups of castrated and noncastrated controls .
### Output Text:
The drug was given to two groups consisting of castrated and noncastrated rats and compared to two groups of castrated and noncastrated controls . 