Final answer:
The stock broker's invitation to Tom points towards an Investment seminar, as it involves professional networking and discussions on investment.
Step-by-step explanation:
The invitation from the stock broker named Nathan to Tom to bring along a few of professional friends suggests a networking or professional development event rather than a purely social occasion. Given the options presented—Business conference, Charity golf tournament, Investment seminar, and Beach vacation getaway—the most likely purpose of such an event by a stock broker would be an Investment seminar. Such seminars are often used for discussing investment strategies, market forecasts, and potentially securing new clients or partnerships among professionals.