The border between the United States and Canada is the longest undefended border in the world, and many lawmakers are starting to argue that if parts of the border are not secured, the citizens of United States have faced an unknown threat.

(A) if parts of the border are not secured, the citizens of the United States have faced an unknown threat.
(B) the citizens of the United States will always face an unknown threat if they did not secure it.
(C) without securing it, the citizens of the United States will always face an unknown threat.
(D) always would the citizens of the United States face an unknown threat if it is not secured.
(E) if parts of the border are not secured, the citizens of the United States will always face an unknown threat.