Are the following sentences natural to a native ear?
1. Was there a dentist at your school today to check the teeth of the students?
2. First finish all the problems. You can do the checking part at once for all the problems. ( I was saying that instead of cross checking every problem after it is solved, the student should first solve all of them and then check them one by one).
3. He enacts scenes in the movie line by line.
No they're not.
1. is almost there, but we wouldn't say 'the teeth of the students'. I'm sure you can think of the alternative.
2. Keep it simple. Just say they can check them all afterwards.
3. If you've watched scenes being enacted in a movie, you can't then enact them yourself. You can only re-enact them.
If I were re-enacting a scene for my friends, I'd do so move by move, rather than line by line. 'Line by line' refers only to the speech, not the actions. But that, of course, means finding another word for 'movie' (...movie move by move). How about 'film'. (A much better word anyway, in my opinion!)