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: On the basis of the findings reported herein , a dose of 60 mg / m ( 2 ) of CCNU combined with 250 mg / m ( 2 ) of CTX ( divided over 5 days ) q 4 wk is tolerable in tumor - bearing dogs .
### Output Text:
On the basis of the findings reported herein , a dose of 60 mg / m ( 2 ) of <span class="chemical">CCNU</span> combined with 250 mg / m ( 2 ) of <span class="chemical">CTX</span> ( divided over 5 days ) q 4 wk is tolerable in tumor - bearing dogs . 