Provide at least listbox instead or small table with
title | author | type

sortable. With search edit box.

Reasons:
a) combobox cannot be scaled with the dialog, so with a lot of entries 
combobox is real pain
b) combobox presents only shortnames
c) you cannot reorder combobox items, putting for example books first
d) you cannot really search anything in combobox

Bottom line is -- combobox is fine for 5-10 entries top, but for real use it 
makes more harm than good.