Final answer:
Contamination occurs when a nonsterile item either crosses over or comes in contact with a sterile field.
Step-by-step explanation:
The correct answer for the question is a) Contamination.
Contamination occurs when a nonsterile item either crosses over or comes in contact with a sterile field. This can happen during medical procedures or when handling sterile equipment.
For example, if a nonsterile bandage comes into contact with a surgical site, it can introduce microbes and lead to contamination.