The volcanoes of many hawaiian island are extinct because

a) the subduction processes that formed the volcanoes have ceased.
b) the pacific plate has carried the volcanoes away from the hot spot that formed them
c) the volcanoes are now below sea level.
d) the hot spot that formed them has moved.

b) the Pacific plate has carried the volcanoes away from the hot spot that formed them

Explanation:

The Hawaiian islands all have volcanic origin. Some are not active, while some still are. All of these islands have been active volcanoes at one point of time, and they have been created by a hot spot that lies beneath the Pacific plate. The hot spot has such a power that it actually manages to break through the central part of the plate where its crust is the strongest and densest. As the magma manages to come out above the water, it manages to create volcanic islands. The Pacific plate though is moving, it is not static, so it drags the volcanic islands away from the hot spot, causing their extinguishing. As those islands are moved away, the hot spot creates new volcanic islands, and the process constantly continuous, resulting in a volcanic island chain.