Hi, i am not sure what (1) and (2) mean. i feel "chem lab" is a shortened version of either a chemical lab or a chemistry lab. in (3), 'grand entrances' refers to the dramatic way the movie stars are introduced in a movie, for example, in the first few minutes of a movie, the hero is shown in a bike-chase scene where he successfully resuces a kid or the heroine from the clutches of a rowdy by performing a super human stunt.
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