The main issue in A apart from 'which' is meaning!
a)
which discusses life among early human tribes, suggests that hunting and foraging groups be viewed as distinct from agricultural communities, rather than as part of a continuum
hunting and foraging groups be viewed as distinct from agricultural communities fine......but
rather than as part of a continuum is not fine!
distinct should be compared or should be parallel to continuum not the 'agricultural communities'!
d) discussing life in early human tribes, suggests that early hunting and foraging groups and agricultural communities be viewed as distinct, rather than as parts of a continuum
This is precisely telling us 'hunting and foraging groups' and 'agricultural communities' were viewed as 'distinct' rather than as parts of 'continuum'.
'distinct' vs 'continuum' is correct!
B) suggests hunting and foraging groups
should be viewed -- Subjuctive verb should have been used therefore 'should' is incorrect.
C) The Gatherers ,.....suggest - SV agreement error
E) Main verb is missing....suggested is not the verb it's the modifier.