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: At the end of the procedure , Group A ( n = 20 ) had 20 mg / 0 . 5 mL of methylprednisolone and 10 mg / 0 . 5 mL of gentamicin injected into the posterior sub - Tenon ' s space and Group B ( n = 20 ) had the same combination injected into the anterior sub - Tenon ' s space .
### Output Text:
At the end of the procedure , Group A ( n = 20 ) had 20 mg / 0 . 5 mL of <span class="chemical">methylprednisolone</span> and 10 mg / 0 . 5 mL of <span class="chemical">gentamicin</span> injected into the posterior sub - Tenon ' s space and Group B ( n = 20 ) had the same combination injected into the anterior sub - Tenon ' s space . 