First conditional .
It’s used to describe things that we think are likely to happen in the future
The Vietcong set up checkpoints around the nation, so that would've definitely been a literal and figurative roadblock to any refugees. Hope this helped.
The correct answer is D.
Stream of conscious narration is an example of experimentation in American modernism. The other techniques were commonly used long before the advent of modernism and would not be examples of experimentation.