beberapa bahan untuk dipelajari :
http://www.4shared.com/document/qGc3249h/What_is_selling_2.html
http://www.4shared.com/document/9VzYNUmK/Critical_communication_skills.html
http://www.4shared.com/document/Jphs_PeA/Communication_Skills.html
http://www.4shared.com/document/pqvQFTks/marketing-vs-selling-120733457.html
