Visibility won't be affected unless whatever the material the bottom consists of is stirred up. The second was a question about ground terrain affecting which factor of a dive, the "supposedly correct" answer was "visibility". I don't recall seeing anything remotely close to a single finger slicing across the neck which is the correct signal for that. The answer - in my opinion- should be "stay at this depth" and yet the "correct" answer was "out of air".
One of them shows a still image with a diver giving a hand signal with a horizontal hand across the chest. I was reviewing the PADI OW final exam questions with my girlfriend and IMHO there are 3 or 4 poorly worded questions or the answers are simply wrong.