The lecture will be in the classroom. The classroom has many desks. 를 한문장으로바꾸면 The lecture will be in the classroom in which has many desks.라고한다네요 근데 which 앞에 왜in이들어가는지 설명부탁드립니다...

그리고 Grapes are raw materials. Wine is made from grapes.를 한문장으로바꾸면 Grapes are the raw materials from which wine is made.가 답이래는데 왜 Grapes from which wine is made are raw materials.가아닌가요?