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: In the motor activity test measured with an Animex - activity meter neither of the K ( + ) - channel blockers affected morphine - induced hypoactivity , but both K ( + ) - channel blockers prevented morphine - induced secondary hyperactivity .
### Output Text:
In the motor activity test measured with an Animex - activity meter neither of the <span class="chemical">K</span> ( + ) - channel blockers affected <span class="chemical">morphine</span> - induced hypoactivity , but both <span class="chemical">K</span> ( + ) - channel blockers prevented <span class="chemical">morphine</span> - induced secondary hyperactivity . 