Final answer:
The technical rehearsal in theater is the time when all the design and technical elements of the production come together. It is during this rehearsal that the safe operation of all scenic shifts, light cue levels and timing, and the placement and length of all sound cues are established.
Step-by-step explanation:
The technical rehearsal in theater is the time when all the design and technical elements of the production come together. It is during this rehearsal that the safe operation of all scenic shifts, light cue levels and timing, and the placement and length of all sound cues are established. This means that all the options provided in the question - the safe operation of scenic shifts, light cue levels and timing, and sound cue placement - are correct.