In which one of the following groups are all the four countries members of G20 ?

Option (a) is correct because Argentina, Mexico, South Africa, and Turkey are all permanent members of the G20, representing a diverse mix of advanced and emerging economies. Option (d) is the most tempting distractor, but it is incorrect because Singapore is not a member of the G20, just as Malaysia, New Zealand, Iran, and Vietnam are excluded in other options. The core concept being tested is the precise membership composition of major global intergovernmental forums and international organizations.