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: Seizures induced by hexafluorodiethyl ether ( HFDE ) were also found to be a more sensitive measure of protection by CBZ than seizures induced by maximal electroshock ( MES ) .
### Output Text:
Seizures induced by <span class="chemical">hexafluorodiethyl ether</span> ( <span class="chemical">HFDE</span> ) were also found to be a more sensitive measure of protection by <span class="chemical">CBZ</span> than seizures induced by maximal electroshock ( MES ) . 