Improved infrastructure enables external economies of scale Steps:

• Identify the change: Improved road links reduce transportation costs for the manufacturer.
• Classify the benefit: This is an industry-wide infrastructure improvement, not specific to one firm's actions.
• Link to economies of scale: External economies occur when external factors like better transport lower average costs for all firms in the area.
• Confirm definiteness: This directly and certainly benefits the firm through reduced costs, unlike other options which may or may not follow.

Why C is correct:

• External economies of scale are cost savings from factors outside the firm, such as public infrastructure improvements like roads, which lower input costs for the entire industry (definition from microeconomics).

Why the others are wrong:

• A: Average revenue depends on price and sales volume, which may not increase despite lower costs.
• B: Internal economies arise from the firm's own expansion (e.g., larger scale production), not external road improvements.
• D: Market share could rise with better access, but competitors may also benefit equally, so it's not definite.

Final answer: C