jQuery show/hide options from one select drop down, when option on other select dropdown is slected same thing has to be come

I need to be select and list only those selected items & need to be visible, which i selected in first selected dropdown.

This is in one form

 <% selected = contract_labour.entity ? contract_labour.entity.entity_name : "" %>
        <%= f.select(:entity_id, @entities.collect {|u| [u.entity_name, u.id]}, {include_blank: "Select Entity"},{ :class => 'form-control required'}) %> 

This is in another form

<%= f.select(:entity_id, @entities.collect {|u| [u.entity_name, u.id]}, {include_blank: "Select Entity"}, { :class => 'form-control required' }) %> 

i have two tabs wre these entity drop downs are present in that

<option> company 1 </option> <option> company 2 </option> <option>
    > company 3 </option> <option> company 4 </option>

if i click on company 1 in first tab means when i enter to second tab in that entity drop should be only display company 1 only not all,

can any one send me the code how to do this since i tried a lot help