Step 1: Understanding the Question: 
The question asks which factor helps determine the 'form' or 'structure' of an organization (e.g., sole proprietorship, partnership, company). 
 Step 2: Analysis of Options: 
Let's evaluate how each factor influences the choice of organizational form. 
    
 (A) Size: The size and scale of operations are major determinants. A small-scale business (like a local retail shop) can be easily managed as a sole proprietorship. However, a large-scale enterprise with significant capital requirements and complex operations is better suited to be a joint-stock company. As the intended size of the business grows, the need for more capital, professional management, and limited liability increases, pushing the choice towards a corporate form. 
    
 (B) Location: The location of a business does not fundamentally determine its legal structure. A company can be located anywhere, and its legal form (proprietorship, company, etc.) is independent of its physical address. 
    
 (C) Study: This is too vague. While a 'study' or analysis is conducted to decide the form, 'study' itself is not a determining factor. The factors are what you study (e.g., size, liability, capital needs). 
 Step 3: Final Answer: 
The size of the business is a crucial factor in deciding the most appropriate legal form of organization. Therefore, (A) is the correct answer.