Step 1: Understand the question.
We must find which PowerPoint tab holds the Rehearse Timings option.
Step 2: What Rehearse Timings does.
Rehearse Timings lets a presenter practise a talk and record how long each slide takes. It is a presentation delivery tool.
Step 3: Group features by job.
In PowerPoint, tools are grouped by purpose. Anything about running and presenting the slides usually sits in one place.
Step 4: Find the right tab.
Since timing the slides is part of giving the show, this option lives under the Slide Show tab, along with start show and set up show.
Step 5: Reject the other tabs.
Insert adds objects, Design changes the look, and Review handles spelling and comments. None of these handle show timing.
Step 6: Conclude.
So Rehearse Timings is under the Slide Show tab, which is option 3.
\[ \boxed{\text{Slide Show}} \]