He has worked the maths problem for nearly an hour but he simply can’t work it .On ;at B. on ;out C. at ;up D. for ;out
__________ the time the firemen arrived, the building had been burnt to pieces.
__________ industry develops quickly, more and more rivers are being polluted.
Most Chinese musical instruments are quite different __________ western ones __________ shape.
His parents are both out of work, so they can't __________ a computer.
The popular band __________ because the members had different opinions on some important matters.