The most accurate way to describe the excerpt is to choose the option - it is a dependent clause. This means that something needs to be added - you need to finish the sentence so that it becomes an independent clause, and not a subordinate one.
I think it would be likely. Britain is a country that is well-developed and has a decent military. If you are referring to war in London or other big cities, I think the armies would try to keep warfare on the battlefield, not urban areas. However, to counter that, (correct me if I'm wrong), I believe London is on the water, so a type of naval invasion would be likely. It also depends on who the fighters are. Britain v. U.S.A. for example, evacuations of cities would begin, and it's likely we'd see another Refugee Crisis like the one happening now in Europe, but smaller. But the U.K is part of the U.N., a huge group of unified countries. If war were to break out, it's likely forces would be pushed out easily with the help of other powers/countries.
B. Both pairs of opposite sides are parallel.
