There were 12 lectures, 6 of which were added that were optional lectures.

共有12节课，其中6节是,补充的选修课。

麻省理工公开课 - 媒体、教育、市场课程节选

Oh, by the way, talking about under enrolled subjects, the complementary subject offered by STS called History, Society, and Solid State Chemistry meets Tuesdays and Thursdays at 11:00 in room 2-136.

顺便说一下，关于已经选了的课，由STS开设的补充课程,历史课，社会社和固体化学课,在2-136教室的11点，在周三和周四上。

麻省理工公开课 - 固态化学导论课程节选