【单选题】The coordinate of a particle in meters is given by x ( t ) = 12 t – 3.0 t 2 , where the time t is in seconds. The particle is momentarily at rest at t = ?
【简答题】A.The third finger is the lucky finger. B.The third finger is the middle finger. C.The third finger is supposed to be linked to the heart. D.The third finger is a symbol of lasting affection.