Hello. I would like to know whether the following sentences (1b,2b) are grammatical or not. Do you think that it is possible to make questions like (1b,2b) from (1a,1b)? (1) a. I saw John enter the building. b. Who did you see enter the building? (2) a. I heard Mary ring the bell. b. Who did you hear ring the bell? Thank you for your cooperation.