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: We recently reported in young healthy subjects that inhibitory cerebellar stimulation enhanced the sensorimotor plasticity of M1 that was induced by paired associative stimulation ( PAS ) .
### Output Text:
We recently reported in young healthy subjects that inhibitory cerebellar stimulation enhanced the sensorimotor plasticity of M1 that was induced by paired associative stimulation ( PAS ) . 