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 worst toxicities ( % ) observed were ( CTC - NCI 1 / 2 / 3 ) : leukopenia 45 . 5 / 18 . 2 / 6 . 1 , thrombocytopenia 33 . 3 / 9 . 1 / 6 . 1 , vomitus 24 . 2 / 9 . 1 / 0 , diarrhea 36 . 4 / 6 . 1 / 3 . 0 , stomatitis 18 . 2 / 9 . 1 / 0 , hand - foot syndrome 12 . 1 / 0 / 0 .
### Output Text:
The worst toxicities ( % ) observed were ( CTC - NCI 1 / 2 / 3 ) : leukopenia 45 . 5 / 18 . 2 / 6 . 1 , thrombocytopenia 33 . 3 / 9 . 1 / 6 . 1 , vomitus 24 . 2 / 9 . 1 / 0 , diarrhea 36 . 4 / 6 . 1 / 3 . 0 , stomatitis 18 . 2 / 9 . 1 / 0 , hand - foot syndrome 12 . 1 / 0 / 0 . 