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: Results presented here show that the differential sensitivities of BS and BR lines to beta - CCM can be extended to diazepam , picrotoxin , and pentylenetetrazol , suggesting a genetic selection of a general sensitivity and resistance to several ligands of the GABA ( A ) receptor .
### Output Text:
Results presented here show that the differential sensitivities of BS and BR lines to <span class="chemical">beta - CCM</span> can be extended to <span class="chemical">diazepam</span> , <span class="chemical">picrotoxin</span> , and <span class="chemical">pentylenetetrazol</span> , suggesting a genetic selection of a general sensitivity and resistance to several ligands of the <span class="chemical">GABA</span> ( A ) receptor . 