When writing a response email, you should open by announcing the most important fact or answer. The Option D.
In this case, by announcing the most important one, its immediately addresses the recipient's primary reason for contacting you and ensures that they receive the critical information right from the beginning. It captures their attention and provides clarity which makes the communication more effective.
By starting with the most crucial piece of information, you demonstrate professionalism and respect for the recipient's time. It allows them to quickly grasp the purpose of your email, setting a positive tone for the rest of the message.
This approach are particularly useful in business and professional contexts, where clear and concise communication is highly valued leading to more productive and efficient email exchanges.