The correct answer is 4.- Only first degree contacts.
The person that can write a recommendation for a person on a professional network site is a first-degree contact.
Network sites are becoming an interesting way of promoting people in the workplace or for different jobs when there are vacancies. Sites like LinkedIn has become a prominent site to create a professional profile and promote yourself in your industry, adding contacts and acquaintances. Many people have moved to other jobs or get better jobs using these networking sites.