In an array based implementation of a balanced binary tree, to check a node stored at array[i] is an external node or not, which of the following statement is true?

A)	return true if array[2i+1] and array[2i+2] is null

B)	return true if array[i/2-1] and array[i/2-2] is null

C)	return true if array[i/2-1] or array[i/2-2] is not null

D)	return true if array[2i+1] or array[2i+2] is not null