Choose the correct answer: Consider the following diagram:

The correct answer is E. 5. Based on the image you provided, the diagram depicts the following sequence of steps involved in creating an order:

Create Order: This signifies the initiation of the order process.

Fill Order Request: This step likely involves gathering information or processing details about the order.

Create Invoice: An invoice is typically generated after an order is finalized.

Notify Customer: The customer is informed about the order, possibly confirmation or receipt.

The key here is that the process starts with creating the order (step 1) and ends with notifying the customer (step 4). Steps 2 and 3 (filling the order request and creating an invoice) can happen concurrently and don't necessarily follow a specific order in relation to each other.

Therefore, following the logic of the sequence, there are five steps (0-based indexing), making E. 5 the most suitable answer.