Final answer:
Digital Certificate is the method that best achieves the objective of ensuring authentication, confidentiality, and non-repudiation when sending sensitive sales quotes.
Step-by-step explanation:
The method that best achieves the objective of ensuring authentication, confidentiality, and non-repudiation when sending sensitive sales quotes is A. Digital Certificate.
A digital certificate is a secure way of proving the authenticity of digital data and verifying the identity of the sender. It also ensures confidentiality by encrypting the data being sent, making it only accessible to the intended recipient. Non-repudiation is achieved through digital signatures, which are part of the digital certificate, and provide a way to verify that the sender cannot deny sending the data.