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: Groups ADR ( 6 ) , ADR + LOS ( 6 ) and ADR ( 12 ) , and ADR + LOS ( 12 ) received ADR ( 2 mg / kg / b . w . i . v . ) twice in a 3 - week interval .
### Output Text:
Groups <span class="chemical">ADR</span> ( 6 ) , <span class="chemical">ADR</span> + <span class="chemical">LOS</span> ( 6 ) and <span class="chemical">ADR</span> ( 12 ) , and <span class="chemical">ADR</span> + <span class="chemical">LOS</span> ( 12 ) received <span class="chemical">ADR</span> ( 2 mg / kg / b . w . i . v . ) twice in a 3 - week interval . 