The United States (US) has hit China where it hurts by going after its telecom champion Huawei, but Beijing's control of the global supply of rare earths used in smartphones and electric cars gives it a powerful weapon in their escalating tech war.A seemingly routine visit by President Xi Jinping to a Chinese rare earths company this week is being widely read as an obvious threat that Beijing is standing ready for action."We should firmly grasp the strategic basis of technological i