The increase in hours they are required to work in an understaffed, unsupportive situation (have angered the nurses at West Branch Home and threatened a walkout).
B) has angered the nurses at West Branch Home and caused them to threaten a walkout
E) has angered the nurses at West Branch Home to have a walkout
the answer is (B) but i don’t know why. (E) is more concise and seems to be grammatically correct as well. HELP MIKE!!!

You just don’t say that something “has angered the nurses … to have a walkout.” You might say exactly what B says, or something like, “…has angered the nurses to the extent that they are considering a walkout,” but E just doesn’t fly.