He has worked __________ the maths problem for nearly an hour but he simply can't work it __________.
A.on;at |
B.on;out |
C.at;up |
D.for;out |
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He has worked __________ the maths problem for nearly an hour but he simply can't work it __________.
A.on;at |
B.on;out |
C.at;up |
D.for;out |