You have an Azure subscription that contains an Azure Cosmos DB for NoSQL account named accounts In account1, you plan to create a container that will store the data items shown in the following table.

Each customer item will have customer sales by month values embedded.

The most executed query will return data for a matrix that aggregates the monthly sales ot each business category. The matrix will use customer business categories as columns and months as rows.

You need to configure the partition key for the container. The solution must minimize the request units (RUs) required to run th e query.

Which property should you use for the partition key?