Hey There,
The option to finish the sentence is option A, Would.
If he were a bird, he Would fly. He is thinking of what he would do if he were a bird, which he is not. The words will, shall and should do not work, because he is not a bird, and therefor he can't fly. He would fly, but he can't.
Best Of Luck,
- I.A. -
"This part of the country"
"western" vs "east" also denotes location, which implies that a region is a specific location in a "part of the country"