Question

Clause Practice Main/Subordinate, which one are they?​

Answer 1

I- what is happening here?

Answer 2

The main would be who and the verb. The subordinate would be the main and what they are doing.

For example the second one:
We waited until everyone arrived.

Ask yourself what are they doing? They’re waiting so the main answer is: We waited

What are they doing? They are waiting until everyone arrives so the answer for subordinate would be: until everyone arrived