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: CONCLUSION : We conclude that patients with osteoporosis can report pain , and bisphosphonate - related pain should also be considered before ascribing this complaint to osteoporosis .
### Output Text:
CONCLUSION : We conclude that patients with osteoporosis can report pain , and <span class="chemical">bisphosphonate</span> - related pain should also be considered before ascribing this complaint to osteoporosis . 