After what seemed to be a long time, the old man went out of the professor's sitting room 是个什..

After what seemed to be a long time, the old man went out of the professor's sitting room 是个什么从句？是如何分析得来的？

what seemed to be a long time 作after介词的宾语，After what seemed to be a long time作时间状语，the old man went out of the professor's sitting room 作主句

after（ what ）seemed to be a long time 介词短语作定语 after是介词 what从句是宾从 the old man 是主句主语 went out of 是主句谓语 the professor's sitting room是主句宾语 之所以选择what，是因为after后面的宾从中缺少主语，能承担这一任务的只有what 供参考。