Answer: Option A
The blood is the least that can harbour commensal microbes.
Step-by-step explanation:
Commensal microbes are microbes that form a relationship with an organism in which one benefits and neither is hurt. These bacteria are necessary for a healthy and developed immune system. They are part of the microplora in the mouth. Commensal bacteria are least in the blood because the blood is a sterile environment and is not conducive for their habitation. The immune response of the blood to the bacteria can cause septic shook which can lead to death.