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: Autism is a neurodevelopmental disorder presenting before 3 years of age with deficits in communication and social skills and repetitive behaviors .
### Output Text:
Autism is a neurodevelopmental disorder presenting before 3 years of age with deficits in communication and social skills and repetitive behaviors . 