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: A step - down passive avoidance paradigm was employed and nefiracetam ( 3 mg / kg ) and apomorphine ( 0 . 5 mg / kg ) were given alone or in combination during training and at the 10 - 12h post - training period of consolidation .
### Output Text:
A step - down passive avoidance paradigm was employed and <span class="chemical">nefiracetam</span> ( 3 mg / kg ) and <span class="chemical">apomorphine</span> ( 0 . 5 mg / kg ) were given alone or in combination during training and at the 10 - 12h post - training period of consolidation . 