Final answer:
The statement is true; external audits in strategy formulation are complex due to the numerous and ever-changing interactions among key external factors.
Step-by-step explanation:
The statement that there are an infinite number of interactions among key external factors during the external audit part of strategy formulation is true. The complexity is due to a variety of external factors like economic conditions, social trends, political environments, technological changes, and legal regulations that a company must consider. These factors are numerous and dynamic, meaning they are constantly changing and interacting in complex ways, which makes predicting outcomes and planning strategy a challenging task.