Approximately what percent of all bacteria are considered harmless to humans?

• A. Over 90%
• B. Around 25%
• C. Less than 10%
• D. About 50%

Answer: (A)

Verified step by step guidance

1. Understand the question: It asks for the approximate percentage of bacteria that are harmless to humans, which means bacteria that do not cause disease or harm.
2. Recall that the vast majority of bacteria in the environment and even in the human body are either beneficial or neutral, playing important roles such as aiding digestion, producing vitamins, or decomposing organic matter.
3. Recognize that only a small fraction of bacteria are pathogenic (disease-causing) to humans, while most are harmless or beneficial.
4. Based on microbiological studies and knowledge, the percentage of harmless bacteria is known to be very high, typically over 90%.
5. Therefore, the correct approach is to select the option that reflects this high percentage of harmless bacteria, which is 'Over 90%'.