i didn't know they would go to Japan 为什么是they would

i didn't know they would go to Japan 为什么是they would
i didn't know they would go to Japan
为什么是they would

i didn't know they would go to Japan 为什么是they would
would在这里作为will的过去时.
这句话的意思是：我不知道他们要去日本.
在这句话中,他们要去日本是已经决定好的事了.所以用过去时.

因为是didn't，时态是过去时，know后面省略了一个that，后面是一句完整的句子，时态也是过去时，所以用would