Final answer:
The Act of Supremacy in 1534, driven by Henry VIII's desire for an annulment from Catherine of Aragon, officially started the split from the Roman Catholic Church, creating the Church of England with Henry as its head.
Step-by-step explanation:
The incident that officially caused Henry VIII to split from the Roman Catholic Church was his desire to annul his marriage to Catherine of Aragon, which the pope refused.
His frustration led to key actions, including Parliament passing the Act of Supremacy in 1534, which established the Church of England with the English monarch as its head. The correct answer to the student's multiple-choice question is (a) The Act of Supremacy.