IgA plays an important role in the surface properties as it maintains the immunity in the mucous membranes and hence called surface antibodies.
IgG is found in blood and extracellular fluid , it prevents any infections enhance is called secretory antibody.
IgD activates the B cells which are then ready to defend the body.
IgM has a pentameric structure but has 10 paratopes.
So the correct answer is 'A, B, C, D'.