itspenthalfanhourworkingoutthepysicsproblem.(保持原意)
it______halfanhour_____him____________outthephysicsproblem.
thephysicsproblem________himhalfanhour
ittakessb.sometimetodosth.不是固定搭配么?为什么能用take...for?
还有spent的主语不是人么?it后应该不能用spent吧?