What relationship does this diagram represent?

		For every "B", there are one or many "A". For every one "A", there are zero or one "B"
		For every "B", there are one and only one "A". For every one "A", there are zero or many "B"
		For every "B", there are one and only one "A". For every one "A", there are one or many "B"
		For every "A", there are one and only one "B". For every one "B", there are zero or many "A"