Defense: China has just tested a new intercontinental ballistic missile that can deliver up to 10 independently targeted nuclear warheads, using technology given to them on President Clinton's watch to launch communications satellites. The Dec. 13 test of the DF-41 was the third for the new weapon. But it marked the first test of a multiple independently targetable re-entry vehicle, or MIRV, technology and raises by an order of magnitude the nuclear threat to the U.S. as China continues its massive arms buildup. And disturbingly, the threat is in large part of our own making. "The DF-4, which could be...