How is the intra-tier transit link connection created between SR and DR for a Tier-0 Gateway?

How is the intra-tier transit link connection created between SR and DR for a Tier-0 Gateway?
A. Manually create a gateway interface and mark it as transit.
B. Automatically created when DR is created.
C. Automatically created when SR is initialized.
D. Manually create external uplink interface and mark it as transit.