Parametrise Dropdown in Web-HTTP/HTML protocol.

I'm unable to create a parameter (using .csv file) for Dropdown in my script. I'm using HTTP/HTML for my script.

Below is my script for dropdown:
    web_custom_request("NonTreasuryDealCapture.aspx_4", 
        "URL=http://{Some URL}", 
        "Method=POST", 
        "Resource=0", 
        "RecContentType=text/plain", 
        "Referer={Some URL}", 
        "Snapshot=t14.inf", 
        "Mode=HTML", 
        "EncType=application/x-www-form-urlencoded; charset=utf-8", 
        body_variable_3, 
        LAST);