So absorbed ________ in the research that she didn’t hear someone knocking at the door.

So difficult ______ it to work out the problem that I decided to ask Tom for advice.

-- You ought to have given them some advice. ---         , but who cared what I asked?

—Cathy, what are you going to do this weekend?—________, I’m going to see my parents in the countryside.

We have been told that under no circumstances　　　　the computer in the office for personal affairs.