Aggregator transformation variable port

What type of expressions can be used in an Aggregator transformation variable port?

Choose Answer

(A)
Aggregate or non-aggregate expressions, provided they are not used together in a single variable port.
(B)
Aggregate and non-aggregate expressions, together in the same variable port.
(C)
Aggregate, non-aggregate and conditional expressions, together in the same variable port, provided that the variable port is also made a "group-by" port.
(D)
Non-aggregate and conditional expressions only.