D, They are old forms of ingredient used in the making of incense primarily used mainly by the wealthy.
Frankincense is a very expensive ingredient in the making of incense it is often burned indirectly by adding it to coal. Though some do not like the scent of Frankincense alone they often used the resin in the making of other types of incense.
Frankincense is a aromatic tree resin formed when they cut the Boswellia tree's bark, they let the sap bleed out and harden, they would then collect this resin, it comes in a variety of grades ( 4 grades I think ) and it is all graded by hand.
D for more information on them click these links [span style="text-decoration: underline;"]Frankincense[/span] [a href="vny!://en.wikipedia.org/wiki/Myrrh"]Myrrh[/a]
Personally I like the Cannabis incense over Frankincense myself, it has a wonderful relaxing Oder.. but the problem with that, is every time I use it the neighbors keep thinking I am smoking marijuana, which I don't. All though when very stressed out another good incense to use is one of the Lavender scented ones
Frankincense is best.. but that is a personal choice it will vary person to person...
Butter on toast or Margarine on toast