Option C is the most robust. It explicitly specifies the target columns and uses `coalesce' to handle cases where `customer_id' might be directly in the root or nested within the 'customer' object. Options A and D are incorrect as they don't select specific fields or handle potential nesting. B is incorrect as it does not use coalesce function. Option E is also incorrect because it doesn't handle cases where 'customer_id' is not nested within a `customer object.