Question

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

Answer 1

B

考查介词。work on从事，忙于；work out解决。句意：他已经做那条数学问题接近1个小时了，但他还没有做出来。