During the opening of the film Casablanca, we hear an airplane approaching and see people looking up at the sky; in the next shot, we see the airplane flying overhead. What continuity editing technique is primarily at work here?

continuity editing technique is Eyeline match

Explanation:

solution

continuity editing technique is Eyeline match

as when we see in film people hear airplane approaching and they they start looking up at the sky and notice airplane flying overhead this is Eyeline match.

because in this technique setting off camera to eyelines for a single shot of different character

as when they shots are cut together than every characters appear correct character with no confusion.

as this eyeline match is film editing technique that associate with continuity editing system

so correct answer is  Eyeline match editing technique