If the desire is to connect virtual network functions together to accommodate different types of network service connectivity, what must be deployed?

Linking is not a defined NFV or SDN term for connecting VNFs together into a service delivery path.

Bridging refers to Layer 2 network connectivity and is not the term used to describe composing VNFs into a service chain.

Service chaining, also called Service Function Chaining (SFC), is the NFV technique of connecting VNFs in an ordered sequence so that traffic passes through each function - such as a virtual firewall, then a load balancer, then an IDS - to fulfill a specific service requirement. It is the standard mechanism for composing multi-function network services from individual VNFs in an NFV architecture.

Daisy chaining is an informal term for serial connections and lacks the orchestration and service-awareness that SFC provides in NFV architectures.

Switching refers to Layer 2 or Layer 3 packet forwarding and is not the mechanism for composing VNFs into a network service delivery path.