Final answer:
To attract outside investors, a company should develop a comprehensive business plan that outlines its strategies, goals, and financial projections, increasing investor confidence in the firm's profitability and management. The correct answer is option A.
Step-by-step explanation:
When a company wants to convince outsiders to invest in the firm, the most effective document to be developed is a business plan. A comprehensive business plan outlines the company's goals, strategies, market analysis, financial projections, and the management team's expertise. This vital information provides potential investors with insights into the firm's products, revenues, costs, and potential profitability, thus encouraging them to provide financial capital to the firm.