Hi,I haven't seen you for a long time.---I__ in Beijing.I've just come back.答案是shall be,was为什么不可以呢

Hi,I haven't seen you for a long time.---I__ in Beijing.I've just come back.答案是shall be,was为什么不可以呢
Hi,I haven't seen you for a long time.---I__ in Beijing.I've just come back.答案是shall be,
was为什么不可以呢

Hi,I haven't seen you for a long time.---I__ in Beijing.I've just come back.答案是shall be,was为什么不可以呢
为什么不是should be ,不是过去式吗……?

时态不同啦，was是过去式。

同问………………