Why was Vietnam’s physical geography a problem for the US?

Can someone list any possible solutions to air pollution ?

When volcanoes erupt, magma (hot, molten rock) rises toward the surface of the earth. as magma cools, solid rock forms. this rock contains substances from the interior of the earth. which of the following natural resources is likely to be plentiful near subduction zones where volcanic activity has occurred in the past?

How many active volcanos are there in nicaragua