She <span>had been working</span> on the project for 2 days before she finished it. So B is the only right one as it's a continuous action before an action with an exact defining past perfect continuous. Also there's a key word "for" that can help us to find out the tense.
They started closing there businesses and only letting certain groups purchase from them
The industrial revolution pertains more relevantly to a history research paper than a literature paper. The revolution encouraged greater reliance on new technology, industrialization, and urbanization instead of the literary arts.
The phrase is talking about a forward-looking reason — a way that the effect fits into a story — your story. In the flat tire case, there was a cause for the tire going flat. Something punctured the tire, causing the air to escape. But, of course, that's a backward-looking reason.
