it spent half an hour working out the pysics problem.(保持原意）
it ______ half an hour _____ him _____ _______out the physics problem.
the physics problem________him half an hour
it takes sb.sometime to do sth.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？