The example of a direct channel where the producer sells directly to the end user is option C: a dentist filling a cavity.
Here's why:
1. In this scenario, the dentist (producer) directly provides a service (filling a cavity) to the end user (patient).
2. There are no intermediaries involved between the dentist and the patient, making it a direct channel.
3. The transaction happens directly between the producer (dentist) and the end user (patient), without any middlemen like wholesalers or retailers.
Therefore, option C, a dentist filling a cavity, is the example of a direct channel where the producer sells directly to the end user.
