Which Step in Implementing Multichannel Marketing Is Most Challenging

Which step in implementing multichannel marketing is most challenging?

A) Establishing subbrands for catalog retailers and direct selling channels.
B) Employing communication and delivery channels that are mutually reinforcing in attracting, retaining, and building relationships with consumers.
C) Monitoring and measuring performance in various channels.
D) Creating a website that will engage visitors with interactive experiences.
E) Documenting cross-channel consumer behavior with a customer journey map.