In Interbank Trading, If a Dealer Is Calling "Off" at the Same

In interbank trading, if a dealer is calling "off" at the same time as the broker is hitting a price:

A) no transaction should be concluded and the broker should inform both counterparties accordingly
B) a transaction should be concluded and the broker should inform both counterparties accordingly
C) the dealer has the choice of either concluding the transaction or not
D) the broker decides whether the transaction should be concluded or not