Answer: The drill's sound
Explanation:
The Conditioned stimulus refers to the event that has been linked with the Unconditioned stimulus to trigger a conditioned response. In this case, the Unconditioned stimulus is the pain felt during dental work. This has become associated with the sound of the drill, leading Jill to feel anxiety whenever she hears that sound.
An astronomical unit (AU) is defined as the distance from the Earth to the Sun, approximately 150,000,000 km, or 1.5 x 10^8 km. In meters, this is 1.5 x 10^11. To convert a distance from meters to AU, one should divide the distance by 1.5 x 10^11. This corresponds to the third option.
Applying the disinfectant once removes 90% of the bacteria, leaving 10% remaining.
Applying it a second time eliminates 90% of that remaining 10%, so you calculate 10 minus 90% of 10 to find the leftover bacteria after two applications.


This results in only 1% of the bacteria still being present, meaning that
99% of the original bacteria have been eradicated.