Two years ago, your community began testing the tornado siren every Wednesday at noon. The first few times, the blaring siren startled you. Now, you barely notice it. This is an example of

This is an example of habituation.

Explanation:

Habituation refers to the decrease in the response to a stimulus after a prolonged exposition to that stimulus. In the situation we are analyzing here, you are experiencing habituation. The stimulus - the sound of the tornado siren - no longer provokes a response from you. When it was a novelty, something you hadn't gotten used to yet, you would be startled. However, after hearing it over and over again, you no longer jump at its sound. You are now habituated to it.

a would be the answer