You can use the list unit, and use a atribute condition o relationship condition.
You should read :
http://www.webratio.com/learn/learningobject/Index-Unit?link=oln72ae.redirect&history=h1&nav=27
http://www.webratio.com/learn/learningobject/Getting-started-with-Selector-Conditions?link=oln72ae.redirect&history=h2&nav=27
http://www.webratio.com/learn/learningobject/Getting-started-with-Selector-Conditions?link=oln72ae.redirect&history=h3&nav=27