Which of the following best describes seamounts and islands of the deep ocean basins?

a. huge granite batholiths intruded beneath the ocean floor
b. domed gabbro intrusions and massive, submarine, rhyolitic, pyroclastic cones andesitic pyroclastic
c. rocks submerged when the mountains sank below sea level piles of basaltic
d. lava flows built up from the ocean floor by multiple, summit and flank eruptions