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: We sent questionnaires about the numbers of each procedure or examination during nine months of investigation period to each local government in 1986 and 1987 .
### Output Text:
We sent questionnaires about the numbers of each procedure or examination during nine months of investigation period to each local government in 1986 and 1987 . 