A data engineer needs to analyze customer preferences and store sales by combining information from two distinct tables. The first table, named favorite_stores, captures the relationship between customers and their preferred stores. The second table, named sales, records the sales amounts associated with each store. Below are the tables used in this task:

Table 1: favorite_stores

store_id	customer_id
a1	c1
a3	c2
a4	c3

Table 2: sales

store_id	sale_amount
a1	200
a2	150
a4	300

The data engineer executes the following SQL query to perform a left join between these tables:

SELECT favorite_stores.store_id, sales.sale_amount FROM favorite_stores LEFT JOIN sales ON favorite_stores.store_id = sales.store_id;

What will be the result set returned by this SQL query?