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 initiated hepatocytes in the liver were assayed as the gamma - glutamyltransferase ( gamma - GT ) positive foci formed following a 2 - week selection regimen consisting of dietary 0 . 02 % 2 - acetylaminofluorene coupled with a necrogenic dose of CCl4 .
### Output Text:
The initiated hepatocytes in the liver were assayed as the gamma - glutamyltransferase ( gamma - GT ) positive foci formed following a 2 - week selection regimen consisting of dietary 0 . 02 % <span class="chemical">2 - acetylaminofluorene</span> coupled with a necrogenic dose of <span class="chemical">CCl4</span> . 