The correct answer is C because Agent Script variables are read-only unless they are explicitly declared with the mutable keyword. A regular variable without mutable can be referenced, but the agent cannot change its value during the conversation. That is exactly why order_id: string = " " is not suitable for capturing the customer’s order number during runtime. To store information gathered from the user, the variable must be declared as a mutable string, such as order_id: mutable string = " " . Option A is wrong because mutability is not the default. Option B is wrong because the declaration itself is valid syntax; it simply creates a nonmutable variable. The runtime failure occurs when the agent or utility attempts to update it.