Other factors being equal, which sensory stimulus is least likely to lead to sensory adaptation?

The correct answer is: the wail of a loud car alarm. 
Sensory adaptation is a term that refers to the changes that stimuli can trigger on the sensory receptors. The process involves changes in the receptors' sensitivity and it is believed that all of the senses exhibit this adaptation. In particular, the sense of touch can quickly adapt to hot and cold stimulation, but not when the stimulus is extremely intense (such as too hot or too cold). Also, our olfactory sense presents the characteristic of odour fatigue. A prolonged exposure to a specific smell leads to a temporary inability to sense this smell and this is a type of sensory adaptation. Finally,
our hearing undergoes a sensory adaptation as well, but not when it comes to sudden, unexpected and instantaneous loud noises. That is why the wail of a loud car alarm will be the least likely to cause sensory adaptation.

The higher you go up the less oxygen there is