When Communicating with Someone Using Electronic Media,and You Wish to Ask

When communicating with someone using electronic media,and you wish to ask a nonrelated question or introduce a nonrelated issue,what is the best way to introduce the topic?

A) Through a new message
B) In a new paragraph in the original message
C) By highlighting the new topic in color
D) By changing the subject line of the email
E) By using a clear opening line to indicate change