Your AWS infrastructure currently has 4 VPC’s. Your company has established an AWS Direct Connect connection from the on-premise to the AWS infrastructure. How many private interfaces would you configure?

Answer options:

A.None. You can use the resources in the VPC in the normal way.
B.One. One Virtual Interface is enough for accessing the VPC’s
C.Four. One Virtual Interface for each VPC
D.Eight. Two Virtual Interface(One for Incoming and one for Outgoing) for each VPC.

Answer - C
For private virtual interfaces, you need one private virtual interface for each VPC to connect to from the AWS Direct Connect connection.
For more information on working with interfaces, please refer to the below URL:
http://docs.aws.amazon.com/directconnect/latest/UserGuide/WorkingWithVirtualInterfaces.html