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: There were no abnormalities or only isolated degeneration in the 1 - or 2 - wk treatment groups , isolated or scattered degeneration in half of the 3 - wk group , frequent scattered degeneration in the 4 - wk group , scattered or focal degeneration in the 5 - wk group , and extensive degeneration in the 8 - wk group .
### Output Text:
There were no abnormalities or only isolated degeneration in the 1 - or 2 - wk treatment groups , isolated or scattered degeneration in half of the 3 - wk group , frequent scattered degeneration in the 4 - wk group , scattered or focal degeneration in the 5 - wk group , and extensive degeneration in the 8 - wk group . 