Collection_select

<%= collection_select(:project, :id,{@arc_projects),:id,:name,options
={:prompt => “–Archived Projects–”})%>

i use this code to retrive archieved project.and its works also…
but if i want to show a dropdown which can take multiple collection
like this below code,but it will not work.
is it is possible in ruby??anybody help me??its urgent.
<%= collection_select(:project,
:id,{@arc_projects,@inactive_projects},:id,:name,options ={:prompt =>
“–Archived Projects–”})%>

if it is possible then what is the write code…pls help urgent…