红、黄、蓝三色棋子一共250枚，黄棋子是红棋子的1/3，红棋子有a枚，蓝棋子有多少枚请选择CBA(S;r5z4B*A(f:n7j3A-K6P,J2C
A．250-a-（1/3）7j3A-K6P,J2C
B．250-a-（1/3）a7j3A-K6P,J2C
C．250-（a+1/3）7j3A-K6P,J2C