The correct answer is (d) Caldera
It is a unique feature of volcano which is formed by the collapsed volcano. When a large amount of magma will erupt, the chambers of volcano would not be able to support the weight of erupted magma, fractures are formed around chambers and the volcano collapse. This is how a caldera is formed.This collapsing of volcano into itself makes it large and a special kind of crater. This makes the magma empty beneath the volcano as a result of large volcanic eruption.