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Magnetic interference from MP3 headphones can interfere with heart pacemakers （心脏起搏器）and implantable defibrillators, a study has found. Heart patients with such devices should not put their headphones in their breast pocket or hang them round their neck, researchers have warned. Small but strong magents inside headphones can deactivate the devices if placed within 1.2 inches of them, posing a real risk to the patient, researchers told an American Heart Association meeting in New Orleans. The MP3 players themselves posed no threat to pacemakers and defibrillators. Dr. William M关于西北地区的地形叙述，正确的是(      ) A．以平原、盆地为主 B．内蒙古高原表面较平坦，风蚀作用显著 C．新疆地形“两盆夹三山”    D．塔克拉玛干沙漠位于准噶尔盆地内