Explanation:

Option A (Social trends) is correct because external factors influencing industry growth encompass macroeconomic, technological, demographic, governmental, and social influences. These are analyzed using frameworks like Porter's Five Forces and PESTLE.

Option B (Barriers to entry) is incorrect as it represents an internal factor affecting an industry, not an external influence.

Option C (Industry concentration) is also incorrect because it is an internal factor, whereas external influences include the broader categories mentioned above.