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 study was designed to have a power of greater than 0 . 90 to detect a slowing to 25 % of the expected rate of progression of weakness at P less than 0 . 05 .
### Output Text:
The study was designed to have a power of greater than 0 . 90 to detect a slowing to 25 % of the expected rate of progression of weakness at P less than 0 . 05 . 