孙爷爷今年a岁,张伯伯今年(a-20)岁,过X年后,他们相差请选择ABC,_0c3]-{,_9y岁。(a8Y(V'e;Z+S.Y(i0P:B6w(S0L,M
A、20(a8Y(V'e;Z+S.Y(i0P:B6w(S0L,M
B、X+20(a8Y(V'e;Z+S.Y(i0P:B6w(S0L,M
C、X-20(a8Y(V'e;Z+S.Y(i0P:B6w(S0L,M