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: Six EMs received 0 . 5 mg of terbutaline s . c . on two different occasions : 1 ) 1 hr after administration of a placebo and 2 ) 1 hr after 150 mg of metoprolol p . o .
### Output Text:
Six EMs received 0 . 5 mg of <span class="chemical">terbutaline</span> s . c . on two different occasions : 1 ) 1 hr after administration of a placebo and 2 ) 1 hr after 150 mg of <span class="chemical">metoprolol</span> p . o . 