Respuesta :
I believe the correct answer would be the first choice: under the Pacific Ocean. You have to think that the Pacific Ocean is very, very deep, and it's bottom is deeper than the Rocky Mountain, the Mississippi River, and the plains. Therefore, the crust won't be as thick under the Pacific Ocean.
Withing the body of text this question was provided for, you should be able to find the passage, "The oceanic crust is thinner and denser than the continental crust."
Answer: The Pacific Ocean