Magento2: Dropdown option in contact page

We add custom option in contact page:

email Template:

           {{trans "Order Number"}}
        {{var data.ordernumber}}
    

           {{trans "Rodzaj zgloszenia"}}
        {{var data.rodzajzgloszenia}}
    

But how to create in field: Rodzaj zgłoszenia dropdown with select option and forward in email selected option?