They _____ so tired if they _____ for a whole day .wouldn't be feeling ; hadn't been walking很明显考的是if 在非真实条件句中的用法 但是那到底是表示对过去还是现在的假设呢.我应该怎样去区分这样的句子呢 我总觉的应该答案是 wouldn't have been feeling ,hadn't been walking 但是没有那个选项或者两样都应该行 .主句表示对现在的假设 从句表示对过去的假设就是表示对过去的假设

嗯，用两个例子说说我的看法吧
例一
A: The kids looks tired.
B: They wouldn't be feeling so tired if they hadn't been walking for a whole day.
这个例子里面，主句从句都是对当下正在发生的事情的虚拟，陈述句转换：They are feeling tired because they have been walking for a whole day.请注意“现在完成进行时”。
例二
A: The kids looked tired.
B: They wouldn't have been feeling so tired if they hadn't been walking for a whole day.
这个例子里面，主句从句都是对过去的虚拟。陈述句转换：They were feeling so tired because they had been walking for a whole day.请注意“过去完成进行时”。
换句话说，你的假设是正确的，换个语境，两个答案都解释得通。

我就是环球雅思的语法老师，相信我，没问题的
时态分类 主句动词 从句动词
与现在的 should/would/could 动词的过去式
事实相反 might + 动词原形 be ---- were
与将来的 should/would/could 动词的过去式
事实相反 might + 动词原形 were to/should + 动词原形
与过去的 should/would/could 动词的
事实相反 might+动词现在完成时 过去完成时

主从句各自按照语意显示的时态使用虚拟语气.
"being tired"是现在的状态,所以be虚拟为would be;"walk"是过去的动作,所以did虚拟为had done.

首先是对现在的假设，才会使得时态是过去将来时
（如果是对过去的假设，那么应该是would not have felt..你说的那种是过去完成进行时，一个基本不用的时态。。

其次后面为什么要用walking 是因为for a whole day的原因。如果是对过去的假设，那么就不能用不惯hadnot been walking 了，而是应该用had not walked
综上所诉，要不就是wouldn't be feeling ; hadn't been walking（对现在）
要不就是wouldnot have felt, hadnot walked(对过去)