Final answer:
Marie has become a shareholder of McBun Development by purchasing 100 shares of stock in the company.
Step-by-step explanation:
Marie has become a shareholder of McBun Development. When someone buys stock in a company, they become a shareholder and have a portion of the ownership in the company. The stock of a company is divided into shares, and Marie's purchase of 100 shares makes her an owner of a portion of McBun Development.