How does Replicat know the structure of the source tables when the target has a different layout?

How does Replicat know the structure of the source tables when the target has a different layout?

A.
GoldenGate trail file contains the metadata of incoming data

B.
Replicat uses an ODBC connection to connect to the source system tables

C.
Parameter file contains table layouts

D.
Discard file contains table layouts

E.
Source Definitions file contains table layouts

Explanation:
http://gavinsoorma.com/2010/02/oracle-goldengate-tutorial-8-filtering-and-mapping-data/