Student or Learner
I don't understand where to use could or could have. The same problem occurs with the usage of should have and should. Also, can we use should in present as well as in past tense?
For example...i want to say
1. Whatever happened should not have happened. (is this right sentence if i am talking about past )
2. I don't know where could she have/has gone (in this sentence can we use " Where can she has gone")
I really don't understand the use of modals especially should, could and would. Please help