Answer:
D. When the subject matter is objective and informative
Explanation:
An email is a way of sending messages between people through internet using electronic devices. So, you should send an email when the subject matter is objective and informative as emails are a good way to share and highlight important information without including a personal opinion, which is specially important in a work environment.
The other options are not valid because when the subject matter is extremely private or sensitive in nature you shouldn't send emails as someone different from the person it was sent to could read it. Besides, when the subject matter is emotional, email is not the best choice as it is written and the words can be interpreted in a different way that doesn't match the sender's intention.
