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: Pharmacokinetic investigations have shown that alkaline diuresis does not alter CB 3717 plasma levels or urinary excretion and that satisfactory urinary alkalinization can be readily achieved .
### Output Text:
Pharmacokinetic investigations have shown that alkaline diuresis does not alter <span class="chemical">CB 3717</span> plasma levels or urinary excretion and that satisfactory urinary alkalinization can be readily achieved . 