testing network elements

for testing network elements which of the below is TRUE

a)Thorough understanding of RFC s/ IETF standards is enough.

b)One has to know design specifications along with standards and specification.

c)Understanding customer requirements is required for acceptance test only and not for system/functional testing.

d)One has to know design specifications along with standards and customer requirements.

e)Network Testing is subjective and depends on interpretation of Specs and inplementation