Which of the following are true statements about B-Trees. Select all that apply. There will be a deduction for incorrect selections.

		a) Leaves can only differ in level from each other by +/- 1
		b) Insertions and deletions are complicated.
		c) Retrieval performance remains relatively constant.
		d) A B-Tree shrinks by deleting at the level of the leaves.
		e) Nodes that are two small are combined with a sibling
		f) A B-Tree grows by adding levels at the root
		g) Nodes are required to have a minimum number of children to ensure fullness.