Answer:
The correct answer is an e-mail.
Step-by-step explanation:
An e-mail allows us to send and receive messages between several computers inside and outside a company, and the rest of the world.
In an email you can include text, images and different types of documents. This means of communication is quite formal, so a human-resource manager will use this means to communicate with his employees, since the relationship between employee-manager is mostly formal.
Another advantage that emails have is that whoever writes it can attach several recipients so they don't have to write many different emails, but will only write one and send it to all the people they choose.
Given this information we can say that the correct answer is e-mail.