Question

buddhism was spread through
siddartha rejecting old traditions.
siddartha preaching his ideas.
changes in philosophy and beliefs.
new ideas being introduced into a culture.

Explanation:

Buddhism (assuming "Buddhism" was misspelled as "Buckthorn" or it's a typo) spread primarily through Siddhartha (Gautama Buddha) preaching his ideas about the Four Noble Truths, Eightfold Path, etc. Rejecting old traditions isn't the main spread mechanism, changes in philosophy/beliefs is vague, and new ideas into a culture is too general. Preaching his ideas (dharma) to others is how Buddhism spread initially.

Answer:

B. Siddartha preaching his ideas.