Answer: The bacteria uses the oxygen present in the mouth.
Explanation:
The plaque that is formed in the teeth is a highly anaerobic bacteria but it can sustain in the environment rich in oxygen. The oxygen is used by the bacteria and there is a absence of oxygen in the teeth.
It is formed in between the teeth which needs oxygen to survive and if remains for tooth for a longer period of time then it began to grow without oxygen.
It basically uses the oxygen available in the mouth and makes the condition anaerobic.
It should be 3! That is the only logical answer to the question...
When the fertilized egg implants somewhere outside the uterus is called ectopic pregnancy
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