A living microbe that has been weakened and is now less virulent is used to create a vaccine. This microbe is considered:

• A. Inactivated.
• B. Toxoid.
• C. Attenuated.
• D. Degraded.

Answer: (C)

Verified step by step guidance

1. Understand the key terms related to vaccines: 'Inactivated' refers to microbes that have been killed, 'Toxoid' refers to inactivated toxins used as vaccines, 'Attenuated' refers to live microbes that have been weakened to reduce virulence, and 'Degraded' is not a standard term in vaccine classification.
2. Recognize that the problem describes a living microbe that has been weakened but is still alive, which means it is not killed or inactivated.
3. Recall that an 'attenuated' vaccine uses a live microbe that has been modified to be less virulent, allowing the immune system to respond without causing disease.
4. Compare the options and eliminate 'Inactivated' and 'Toxoid' because they involve killed microbes or toxins, not live weakened microbes.
5. Conclude that the correct classification for a living, weakened microbe used in vaccines is 'Attenuated'.