How can delivering mail as text instead of html help prevent spam?

Antivirus signatures are constructed using with of the following?

Which of the following can prevent virus infections?

In a compromised system, which of the following provides the safest way to analyze it?

Which of the following is true of macro viruses?

Which of the following characteristics classify a mail message as spam?

Which technique is used by spammer to find valid/existent email address?

Which is famou worm attack?

Which antispam measure is taken to reduce spam?

What is S/MIME?

How many keys are required if two parties communicate using Symmetric Cryptography?