Answer:
F. After sentence 10
Step-by-step explanation:
To begin with, this is paragraph 3:
"(8) The AquaDom has some other features like a two-floor elevator that is transparent. (9) It allows visitors to ride up the length of the tank to gaze at the fish from every possible level. (10) Though one might guess that the elevator rides along the outside of the tank, it is actually situated in the tank’s center, the clear walls giving riders a truly up-close-and-personal experience with the aquatic residents. (11) The elevator lets visitors observe the dedicated tank divers hard at work. (12) This includes watching the divers feed the inhabitants and clean the massive tank. (13) Getting an inside look at people performing this unique job is as interesting as watching the swarms of fish."
Now, if we add the sentence Ken wants to add to the third paragraph, he should rewrite it like this:
"(8) The AquaDom has some other features like a two-floor elevator that is transparent. (9) It allows visitors to ride up the length of the tank to gaze at the fish from every possible level. (10) Though one might guess that the elevator rides along the outside of the tank, it is actually situated in the tank’s center, the clear walls giving riders a truly up-close-and-personal experience with the aquatic residents. (F) Although this 360-degree view allows people to watch the fish from practically anywhere inside their watery habitat, visitors can catch a glimpse of much more than fins, gills, and tails. (11) The elevator lets visitors observe the dedicated tank divers hard at work. (12) This includes watching the divers feed the inhabitants and clean the massive tank. (13) Getting an inside look at people performing this unique job is as interesting as watching the swarms of fish."
See how it makes a lot more sense? Therefore, your answer is F.
I hope this is helpful!（‐＾▽＾‐）