Answer: core service
Explanation: In simple words, core service refers to the services that are of high importance to the transactions and the business of the rendering firm depends on such services. In other words, it is the main product that the business offers to their customers.
These services renders the benefits that a customers expects to get from his or her purchase. In the given case, Team builds in involved in services in which they provide session that shows how one group should work together.
Hence improved work team is their core service.