Which of the following is the best opening sentence for a business letter that you want to sound fairly informal?

APlease be advised that I've just received your order.
BYour order of February 10 arrived in our office today.
CThis letter is to make you cognizant of our receipt of your order.
DI am in receipt of your order of February 10.

Verified Answer :

The best opening sentence for such a business/informal letter is B. Your order of February 10 arrived in our office today. This is the only sentence that doesn't sound too formal and use a bunch of fancy words in order to make it seem more formal, which is the reason why it is the least formal, in this case and thus the correct answer.