I would say that C and D are some of the northern European countries ie Norway, Sweden, Finland and Poland, Hungary and Romania. Countries like Italy, Spain, France and Ireland would be in southern Europe by comparison.
<span>Vulcanian-type eruptions are common first phases in the eruptions of volcanoes as they "clear their throats" before emitting larger eruptions.They are small and short eruptions but they tend to be violent explosions of viscous magma. They can be repetitive and go on for days to years long.</span>
The plate boundary is the result of movements in the latest either through the divergence, convergence or the formation transform or rift valleys. The occurrence of the earthquakes and volcanic eruptions around the zones of mountain belts and various other events led to the volcanic arcs.
A Mountain belt-like system of the Himalayas in Northern India is a result of the orogenic upliftment of sediments bright from the Tethys sea and splitting of the Indian subcontinent from the Australian plate to collide with the Eurasian plate.
A continental volcanic arc forms due to the lava a magma that originates in the form mantle plums produced due to the burning of the lighter plate over the oceanic plate and volcanoes like the Andes form when the slab pulls the plate to the deep trenches.
And the san Andreas fault in California is a transform fault with dextral movements on both sides as the landmass is drifting westwards.
