Which of the can't spread virus
A plain text mail can't spread virus.
Viruses can easily be transferred from one computer to another through sending mails. This is the most common way used nowadays. They may come as an attachment along with the emails. It is a common opinion that all the spam mails are only virus infected, but it is not so.
HTML stands for HyperText Markup Language. It's the way web pages and email templates are coded so that text is formatted and images are added. Plain Text is regular text, with no formatting options such as bold, italics, underlines, or special layout options.
Most viruses, Trojan horses, and worms are activated when you open an attachment or click a link contained in an email message. If your email client allows scripting, then it is possible to get a virus by simply opening a message. It's best to limit what HTML is available in your email messages.