If a Domain Contains Only Two Nodes, Which Configuration Below

If a domain contains only two nodes, which configuration below is not allowed?

A) Both nodes are gateway nodes at the same time, with Informatica automatically deciding which is the master gateway when the domain is started.
B) Both nodes are worker nodes at the same time.
C) One node or a master gateway, the other is a worker.
D) Only one node is active and it is the master gateway node.