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: In the mouse passive - avoidance test , PG - 9 ( 10 - 30 mg / kg , i . p . ) , administered 20 min before the training session , prevented amnesia induced by both the non selective antimuscarinic drug scopolamine and the M1 - selective antagonist S - ( - ) - ET - 126 .
### Output Text:
In the mouse passive - avoidance test , <span class="chemical">PG - 9</span> ( 10 - 30 mg / kg , i . p . ) , administered 20 min before the training session , prevented amnesia induced by both the non selective antimuscarinic drug <span class="chemical">scopolamine</span> and the M1 - selective antagonist <span class="chemical">S - ( - ) - ET - 126</span> . 