Final answer:
The Cleansweep Broom Company applies oil and wax option (a) to their Cleansweep Eleven broomstick to improve performance, ensuring speedy and smooth flights.
Step-by-step explanation:
The Cleansweep Broom Company applies oil and wax to their Cleansweep Eleven model of broomstick to enhance its performance. This treatment helps to improve airflow around the broomstick, allowing for speedier and smoother flights.
Broomsticks in the Harry Potter series, such as the Cleansweep Eleven, are known for their various enchantments and enhancements to aid witches and wizards in flying. While other options like fireproofing and scented charms can be applied to broomsticks, the specific model in question uses the oil and wax treatment method for its performance benefits.