In August 1986,a Gigantic Volume of CO₂ Belched Forth from Lake

In August 1986,a gigantic volume of CO₂ belched forth from Lake Nyos in Cameroon and swept down the adjacent valleys asphyxiating 1,700 people.The origin of this gas was _____________.

A) a basaltic magma in the subsurface
B) a sub-lake pyroclastic flow
C) an earthquake preceding the volcanic eruption broke a gas pipe running along the bottom of the lake.
D) the calderas collapse of a volcanic dome at the bottom of the lake