曾执教于北京大学用英语怎么说？

先正视听，第一和第四个都是被动语态，说起来有点怪，像在北大受教育多一点；teach的过去分词是taught而非teached；
而曾执教于北京大学则可以用has lectured / has taught at Beijing University （曾在北大任教，现在也是）或had lectured / had taught at Beijing University （曾在北大任教，现在已经离任）

i had teached in beijing university~

Had been taught at Peking University

I have once been in the faculty of Peking University.

曾执教于北京大学
Had once been taught at Beijing University