Drop down in link_to button Rails

I've a view page Of student portal and i have certain buttons on the page in which i've defined action and controller , and now i want to give a dropdown view with these buttons and define action in them.

.pull-right
  #average_mark
     = link_to("Average Mark", {:controller => "student", :action => "average_marks", :academic_year => detail[:year]}, class:'btn btn-primary')
.pull-right
  #highest_mark
     = link_to("Highest Mark", {:controller => "student", :action => "highest_marks", :academic_year => detail[:year]}, class:'btn btn-primary')