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 incidence of subependymal cysts in infants exposed to cocaine prenatally was 44 % ( 8 of 18 ) compared with 8 % ( 8 of 99 ) in the unexposed group ( p < 0 . 01 ) .
### Output Text:
The incidence of subependymal cysts in infants exposed to <span class="chemical">cocaine</span> prenatally was 44 % ( 8 of 18 ) compared with 8 % ( 8 of 99 ) in the unexposed group ( p < 0 . 01 ) . 