Eruption Columns, Such as the One Pictured Above, Are Unstable

Eruption columns, such as the one pictured above, are unstable and often collapse towards the Ground because_______ .

A) they consist mostly of gases, which can cool and descend
B) they are mostly large pyroclastics and these cannot be supported by rising air
C) they are propelled by the eruption, as in the case of Pompeii
D) they are mostly liquid lava flows being lifted by updrafts