it could be mrs smith，because she is in red today.为什么用could而不是m

could be /might be

could 是can 变化过来的；

might是may变化过来的；

从语气上来分别的话，can 比may更加确定，几乎可以说就是她不是别人。而may更加有猜测的意味在里面。

It could be argued

可以说

例句

1.On the one hand, it could be argued that the police failed in the first instance.

而另一方面，可以说，警方在第一时间是失败了。

2.It could be argued that such a smoothing of rent rises is good for existing tenants.

有人可能认为这种租金的平稳增长对现有的租户是有利的。

3.It could be argued that enzymes are the missing link in the modern diet.

可以这样说，在现代饮食结构中，酶是缺损的一环。