Which explains why U.S. leaders are eager to get North Korea to sign the Nuclear Nonproliferation Treaty?

ANorth Korea has targeted U.S. allies with threats of nuclear attacks and ultimate destruction.
BNorth Korea has launched a nuclear attack against the United States in the past.
CNorth Korea has demonstrated that it has access to more nuclear weapons than any other country.
DNorth Korea has the ability to fire a nuclear weapon that could reach U.S. territory.