The answer to the question is (A) overhead projector.
Since Jackson only has three employees who signed up to attend the seminar on how to file taxes, he can choose to use overhead projector in presenting his seminar. This is a better option than webcast, video conferencing, or external monitor. External monitor might be to small for him to effectively present the material to the audience, while webcast and video conferencing might be inefficient if used for something that only has a small number of audience.
