系动词没有时态的变化吧？

Of course, it is.

For instance,
一般现在时: He is here now.
现在完成时: He has been there.
一般过去时: He was there at that moment.
一般将来时: He will be there soon.
...

多了去了.具体情况具体分析

系动词也有时态的变化。
It's very cold now.But tommorrow it will get warmer.

What is pseudo bulbar palsy? There is very little information online about it.?

为什么不可以？