Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE INVOICES (Product_ID VARCHAR)
### Question:
What is the product ID of the most frequently ordered item on invoices?
### Answer:
SELECT Product_ID FROM INVOICES GROUP BY Product_ID ORDER BY COUNT(*) DESC LIMIT 1