Suppose that only numbers in $1...1000$ appear as keys in a binary search tree. While searching for $500,$ which of the

following sequences of keys could not be examined?

A$.200,700,600,300,400,500$

B$.300,400,900,800,500$

C$.700,200,600,550,500$

D$.100,1000,200,800,300,900,500$