In the circular flow diagram, firms receive A. goods and services from product markets.
However, it's important to note that firms also provide goods and services to product markets in exchange for money, which they then use to pay for the factors of production in the resource market. So, if the question were asking about what firms receive from households via the product markets, the answer would be goods and services. But if considering what firms earn from selling their offerings in product markets, the answer would be D. revenue.
In summary, the answers can vary based on the perspective of the flow being considered.