He tried his best to solve the problem, ________ difficult it was.
______ the police thought he was the most likely one, since they had no exact proof about it, they could not arrest him.
Either you or one of your students ______ to attend the meeting that is due tomorrow.
You and I could hardly work together, _____ ?
Please do me a favor — ______ my friend Mr. Smith to Youth Theater at 7:30 tonight.
— It’s the office! So you ______ know eating is not allowed here. — Oh, sorry.