Which of the following best describes common causes?

The choice that best describes common causes is inherent variations in a process. In any process, there will always be variations that occur due to the system's structure and how it operates. These variations are considered "common causes" because they are part of the underlying system and are generally stable and predictable over time.

Understanding common causes is crucial in quality management and improvement. These are the everyday variances that any process experiences, and they represent the baseline level of performance inherent in the process itself. When a process operates normally, it will show variability, but this variability is not necessarily a signal of a problem.

In contrast, the other options highlight different concepts. Temporary variables that affect consistency refer to special causes, which are not part of the inherent variations of a process. Unpredictable occurrences causing defects also allude to special causes rather than the persistent system-level variations captured by common causes. Similarly, errors that occur sporadically hint at occasional issues related to specific incidents or problems, which again are categorized as special causes.

By identifying and understanding common causes, organizations can implement processes to manage these inherent variations effectively, leading to improved stability and quality in performance.