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: Since the introduction of angiotensin converting enzyme ( ACE ) inhibitors into the adjunctive treatment of patients with congestive heart failure , cases of severe hypotension , especially on the first day of treatment , have occasionally been reported .
### Output Text:
Since the introduction of <span class="chemical">angiotensin converting enzyme ( ACE ) inhibitors</span> into the adjunctive treatment of patients with congestive heart failure , cases of severe hypotension , especially on the first day of treatment , have occasionally been reported . 