Step 1: Understanding the Concept:
This is a Critical Reasoning question asking for a necessary assumption of the argument. The argument's conclusion is that sales will be high because customers will be "forced to buy" to avoid getting wet. We need to identify an unstated premise that must be true for this conclusion to hold.
Step 2: Detailed Explanation:
The Argument: People exiting a subway into the rain will be forced to buy a higher-priced umbrella.
The Conclusion: Sales will be greater than normal.
The Logic Gap/Assumption: The argument assumes that the people exiting the subway are vulnerable and have no other option. What would make them have no other option? The most obvious reason is that they don't already have an umbrella with them. If they did have an umbrella, they would not be "forced" to buy a new, higher-priced one. The plan's success depends on the customers being unprepared.
Let's analyze the options:
(A) This is a reasonable statement, but not the core assumption. The argument is about why people \textit{will} feel pressure, not about those who won't.
(B) Profitability of normally priced umbrellas is irrelevant to the sales prediction of the new plan.
(C) The normal sales volume isn't the key assumption; the plan just predicts sales will be \textit{greater} than normal.
(D) The company's other business operations are not relevant to the prediction.
(E) This is the correct answer. It directly addresses the core assumption. If potential customers already had an umbrella, they would not be "forced" to buy a new one. The plan relies on the customers' lack of a pre-existing umbrella.
Step 3: Final Answer:
The success of the marketing plan depends on customers being caught in the rain without an umbrella, making them a captive audience. Option (E) is the assumption that these potential customers are indeed unprepared.