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: Exclusion criteria were asphyxia , malformations , major surgical interventions , small for gestational age , intraventricular haemorrhage grades III and IV , periventricular leukomalacia , and severe psychomotor retardation .
### Output Text:
Exclusion criteria were asphyxia , malformations , major surgical interventions , small for gestational age , intraventricular haemorrhage grades III and IV , periventricular leukomalacia , and severe psychomotor retardation . 