Answer:
The correct answer is: "A. Make sure you provide all the details in a clear manner, even if the e-mail seems long".
Step-by-step explanation:
The best way to write an e-mail is by providing details as much as possible, even though the e-mail seems long, but it may not be, actually, because there are some important informations that must be included in the e-mail and cannot be left unsaid. These important informations need to be clear and very well organized in order to be understood with no trouble. Therefore, all other options are lacking in some way for they seem unclear and not reasonable.