Option A is the best option. If Rachel knows how many slides she need, by this she will get a plan for time she need to give to per slide and she can come up with whole presentation done in 30 minutes.
Explaination :
Option B is not good option because here number of slides is the constraint when she knows how much time she will spend on per slide. Also, she should explain the topic by the time she has not by the number of slides.
Option C, again option C uses the number of slides as major constraint.
Option D, reducing the content can cause problems with quality of presentation as she would not be able to explain much.
Option E, she will have to spent time to edit the layouts because mostly layouts are not that friendly.