Petroleum. For details about the chemistry you might wish to consult the benzene page on wikipedia.
Comets have two main sources, the Oort Cloud or the Kuiper Belt
The two main sources of genetic information are DNA and RNA. DNA carries the genetic instructions for all living organisms, and RNA helps in the process of translating these instructions into proteins.
A major source of conflict in the Muslim Middle East is the divisive nature between the two main sects of Islam: Sunni and Shi'a. Although these two sects agree on the fundamentals of Islam and the teachings of the Quran, they are in conflict about who would lead the Muslim community after Muhammad's death.
The two main sources of genetic variation are gene shuffling and mutations. A mutation is a process wherein the structure of a gene is altered.
I'd have to say Christianity for certain and with the rise of Islam, then Islam is number two.
Islam or Christianty
The two main groups of Islam are the Shia and Sunni. They divided into these groups after Mohamed died and they could not decide on just one successor.
The holy Quran & the Hadith are the first main sources of legislations in Islam,respectively.
The two main branches of Islam in Iraq are Sunnis and Shiites. However, both branches share many common Islam principles and rules. Refer to related question below.
The two main sources in water vapor are farming and manufacturing
islam
Christianity and Islam
It is Islam religion. Muslims are belonging to the main two different schools: Shiites and Sunnis.
The two main sources of air pollution are the toxins released from factories and automobiles.
they are two sect or fraction of Islam religion. Sunnism as Majority and Shiite as minority are two main sects in Islam religion.
it is more accurate in religious sciences if we apply sect instead of branches.therefore we have to say in Islam religion we have two sects,shiite as minority and Sunni as majority.Sunni and shiism are two main sects of islam religion.