Contamination of an experiment by microbes can occur because:

• A. Airborne microbes are too large to enter laboratory spaces
• B. Microbes cannot survive outside their natural environment
• C. Sterile techniques are not properly followed
• D. All laboratory equipment is always microbe-free

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the context of microbial contamination in experiments. Contamination occurs when unwanted microbes enter the experimental setup, potentially affecting results.
2. Step 2: Evaluate each statement given in the problem to determine its validity based on microbiological principles.
3. Step 3: Analyze the statement 'Airborne microbes are too large to enter laboratory spaces.' Consider that microbes, such as bacteria and fungi spores, are often small enough to be airborne and enter lab spaces, so this statement is false.
4. Step 4: Consider the statement 'Microbes cannot survive outside their natural environment.' Many microbes can survive on surfaces or in air for varying periods, so this statement is also false.
5. Step 5: Recognize that 'Sterile techniques are not properly followed' is the correct cause of contamination, as improper sterile technique allows microbes to enter and contaminate experiments, while 'All laboratory equipment is always microbe-free' is false because equipment can become contaminated if not properly sterilized.