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: Our study confirms that RD is effective and safe in RRMM in the RW ; it produces durable responses especially in patients who continue on treatment till progression and improves humoral immunity even in patients with stable disease .
### Output Text:
Our study confirms that <span class="chemical">RD</span> is effective and safe in RRMM in the RW ; it produces durable responses especially in patients who continue on treatment till progression and improves humoral immunity even in patients with stable disease . 