What puzzles me most is why so many students bury themselves in piles of maths exercises _________they should spare some time to reflect on their previous mistakes.

The manager was worried about the press conference his assistant ______ in his place but luckily, everything was going on smoothly

The belief that the children of working mothers usually suffer isby most scientists

Would you please lend me some paper—Sorry, but we have all the paper.

He has never been to Hong Kong before, has he —- . He has been there many times.