Final answer:
It is most appropriate to use written communication when speaking to deaf professionals, as not all may know ASL or can lip-read, and speaking louder is not helpful.
Step-by-step explanation:
When talking to a group of known and unknown deaf professionals for the first time at a work conference, it is appropriate to use written communication. This allows for an inclusive form of communication that everyone can understand, regardless of their preferred mode of communication. While some may use American Sign Language (ASL), not all deaf individuals may know ASL, and it's incorrect to assume that all deaf individuals can lip-read effectively. Additionally, it's inappropriate to speak louder than usual as it does not aid individuals who are deaf. The primary consideration should be to ensure that communication is accessible to all, which can be achieved through writing, whether it's on paper, through text, or any other visual form of conveying messages.