Explanation:

"Juan de Fuca plate is largely responsible for the volcanoes that dot the Pacific Northwest of the United States." - This statement is true. The Juan de Fuca Plate is a tectonic plate that subducts beneath the North American Plate along the Cascadia Subduction Zone, leading to volcanic activity in the Pacific Northwest.

"There are three types of plate boundaries: divergent, convergent, and conservative." - This statement is true. The three primary types of plate boundaries are divergent (plates move apart), convergent (plates move toward each other), and transform/conservative (plates slide past each other).

"All volcanoes and earthquakes in the world are located at plate margins." - This statement is not correct  While many volcanoes and earthquakes are associated with plate boundaries, not all of them are located at plate margins. Intraplate earthquakes and volcanic activity within plates away from plate boundaries can also occur.