Answer:
d. Word of mouth
Step-by-step explanation:
In the given instance it is very clear that there is an announcement in the seminar. This clearly represents the word of mouth. As there is no job posting officially on the web site or newspaper. Also there is no recommendation from any supervisor that there is any need to get a person recruited and this is the person.
In fact there is a straight announcement to ensure the recruitment vacancy. This is the basic conclusion from such scenario and this will be termed as Word of mouth.