Emad Ragheb posted:
Can you explain this sentence please :"There were so many people that I didn't know who was doing what."
The "that"-clause relates to "so." As a result of there being a lot of people there, you didn't know who was doing what.
"Who was doing what" is an embedded question with two wh-elements and is functioning as the object of "didn't know."
You didn't know the answer to the question "Who is doing what?" (i.e., Who is doing this?, Who is doing that?, etc.).
Q: Who is doing what? I can't tell. / I can't tell who is doing what.
A:John is shaking Mark's hand. Joan is setting the table. Mary is reading a book. Billy is jumping on the trampoline. Jill is playing with her dolls.