Final answer:
Option C is the correct statement. A failure is observed as an error and the root cause is the defect.
Step-by-step explanation:
The correct statement is option C. A failure is observed as an error and the root cause is the defect. In the context of software development or testing, an error refers to a mistake in the code or logic that may lead to unexpected behavior. When this error manifests and is detected during testing or usage, it is referred to as a failure. The defect is the underlying issue or bug in the software that causes the error or failure to occur.