分类：教育/科学-学习帮助
问题：关于语态和时态的一道题
--Sorry,sir,I can't answer this questn.--Well,you're supposed_____this part of history.为什么填to have read而不填to read？谢谢！
回答：be supposed to have done 是"本来应该"的意思,相当于should have done