A Fifteen-Foot Tree Growing in a Fence Row Is Used

A fifteen-foot tree growing in a fence row is used as a fence post,to which barbed wire is stapled at a height of five feet.Years later,the tree is thirty feet high.The fence is

A) twenty feet up because it added fifteen feet to the original five-foot height.
B) split because the trunk grew up but the bottom stayed at ground level.
C) fifteen feet up because the tree doubled in height.
D) twenty feet up,still ten feet from the top of the tree.
E) approximately five feet up since a tree grows longer at the tips of its stem,branches,and roots.