JEE servers use Proxy mechanisms to obtain references on EJB objects through business interface. With proxy, container can react on some properties thirled to business methods like @TransactionAttribute or @RolesAllowed.
Even if you return reference on Bar interface it will not be business interface connected to EJB object, so probably you get an exception when you invoke some method from it. That is why answer A) is wrong. Try java.lang.reflect.Proxy for more details. It is great fun.
C) and E) are wrong because lookup method will return reference to the new EJB object, not the same used for method invocation.