The correct answer is A) Prime Minister.
The leader of the majority party in the House of Commons is usually Britain's Prime Minister.
The most important political figure in Great Britain is the Prime Minister. Of course, Queen Elizabeth is a traditional figure that represents the union and tradition of Great Britain, but the Prime minister is the one who rules the nation with the British Parliament. The Prime Minister supervises the Civil Service, the agencies of the government, and is the main figure in the British House of Commons.