What are four causes of the American Revolution and why?

I would suggest, in answering this question, that you consider that the road to the American Revolution was ultimately a long, gradually evolving process. The American colonists did not simply wake up one day and decide they no longer felt like being British subjects.
Ultimately, I would suggest that at the heart of the break with Britain was a shift in British colonial policy, shaped by the impact of the French and Indian War. Before the French and Indian War, Britain practiced a policy known as salutary neglect. There were mercantile laws on the books and certain expectations in play, but in practice, the difficulties of actually governing and administering the colonies across the Atlantic (given the technological limitations available) made the effort of strictly enforcing those laws not worth the costs accrued. With that in mind, traditional British policy towards its colonies was one of general autonomy. After the war with France, however, this calculus swiftly changed, and Britain began more strictly enforcing those mercantile laws and imposing taxes on its colonies, creating resentment and anger among colonists. This resentment can be seen displayed in the famous rallying cry, "no taxation without representation."
This change in policy was one of the most significant long-term driving factors of the American Revolution (and it particularly hurt the interests of the colonial merchant elites). At the same time, as turmoil and resistance began to build within the colonies, Britain responded with a show of force. Soldiers were sent to maintain law and order, which only further inflamed tensions. We can also point towards the so-called Intolerable Acts, which were passed in response to the Boston Tea Party, that only further rallied Colonial complaints of British tyranny and further resistance.
At the same time, we should be aware of the intellectual underpinnings of the American Revolution. Enlightenment principles are embedded deeply within the Revolution, and within post-Revolutionary politics, and these ideas had been circulating for decades within educated circles, both in Europe and in the Colonies. The circulation of this discourse certainly helped contribute to the Revolutionary Movement as it continued to evolve.
Finally, I would suggest you consider the actions and discourse of the Revolutionaries themselves, and the various ways in which they organized and advance their cause. They were very energetic, and as the years moved closer to the outbreak of the American Revolution, they became more and more radical in their ideology and intentions, a process which culminated in the calls for independence.