The underlined word in the sentence is "stimulating." To find the opposite meaning of "stimulating," we need to evaluate each option provided.
Option 1: "Arousing" is a synonym of "stimulating," meaning it has the same or similar meaning. Therefore, it is not the opposite.
Option 2: "Invigorating" is also similar in meaning to "stimulating," so it is not the opposite.
Option 3: "Boring" is the selected answer. It is the opposite of "stimulating" as it suggests something dull, uninteresting, or lacking in excitement.
Option 4: "Stirring" is similar in meaning to "stimulating," so it is not the opposite.
Therefore, the correct answer is option 3: "boring," as it is the opposite of "stimulating."