You need to ensure that all of the email messages queued on Server3 and Server4 are delivered to the Internet as quickly as possible

You have an Exchange Server 2013 organization named adatum.com. You have a database
availability group (DAG) that contains four Exchange servers named Server1, Server2,
Server3, and Server4. The file share witness is on a server named Share1. The organization
has two Send connectors. The Send connectors are configured as shown in the following table.

Users report that email sent to external recipients is not being received. You discover that
outbound email messages are queued on Server3 and Server4. You need to ensure that all
of the email messages queued on Server3 and Server4 are delivered to the Internet as
quickly as possible. What should you do?

A.
Modify the cost of External.

B.
Disable External1.

C.
Modify the list of source bridgehead servers of External2.

D.
Modify the cost of External1.