Public attention at the moment is ______ on the problem of how to create opportunities for the laid-off workers.
He has worked __________ the maths problem for nearly an hour but he simply can't work it __________.
The energy Jenny Bowen has devoted in the past ten years __________ the orphans has been considered __________ of great help.
The __________ on his face told me that he was angry.
Lucy asked for a separate room so that she could avoid __________ with Tom alone.
—What do you think made Mary so upset?—__________ her new bicycle.