name of the grammatical structure

Please help with this:

**Name of the grammatical structure:

must have been.......**

This is the question i've been given and I'm finding it difficult to find the answer.

I've been instructed not to worry about the rest of the sentence.

But the rest of the sentence is : It must have been so frightening for Malak to see her mum so ill.

Solution 1:

I'm not sure if it has a specific name. But usually I refer to this topic as "Modals of deduction"(usually about present or future).

Exactly for your example it's "modals of deduction in the past".

When we say, "You must have been tired"(Because you worked hard that day), this is just our guess about the most possible past event or condition.