Read this and answer the question. If the question is unanswerable, say "unanswerable".

Pre-sectarian Buddhism is the earliest phase of Buddhism, recognized by nearly all scholars. Its main scriptures are the Vinaya Pitaka and the four principal Nikayas or Agamas. Certain basic teachings appear in many places throughout the early texts, so most scholars conclude that Gautama Buddha must have taught something similar to the Three marks of existence, the Five Aggregates, dependent origination, karma and rebirth, the Four Noble Truths, the Noble Eightfold Path, and nirvana. Some scholars disagree, and have proposed many other theories.

Was is the earliest phase of buddhism?
Pre-sectarian