12. 如圖所示,假設電容無初始儲存能量,當 t = 0 秒時將 K 扳至 a 點,若在 t = 30 秒時瞬間將 K 扳至 b 點,則 t = 40 秒時,iC為多少安培 ( A ) ?(A)-1mA(B)-0.64mA(C)-0.32mA(D)-1.35mA