Questions: Which of the following statements about time fences for capacity requirements planning is/are true? They are used to prevent system nervousness. The closest time fence is the most restricted. It is better to have a longer "frozen" period to ensure system stability. The planning fence is closer than the demand fence.

The answer is the first one: They are used to prevent system nervousness.

Explanation for each option:

1. They are used to prevent system nervousness.
   This statement is true. Time fences are used in capacity requirements planning to prevent frequent changes in the production schedule, which can lead to system nervousness. By setting time fences, companies can stabilize their production plans and reduce the impact of last-minute changes.

2. The closest time fence is the most restricted.
   This statement is true. The closest time fence, often referred to as the "frozen" zone, is the most restricted because it is the period where changes to the production schedule are minimized or not allowed. This helps ensure that the production process is stable and predictable.

3. It is better to have a longer "frozen" period to ensure system stability.
   This statement is not necessarily true. While a longer "frozen" period can provide more stability, it can also reduce flexibility and responsiveness to changes in demand or other factors. The optimal length of the "frozen" period depends on the specific needs and circumstances of the organization.

4. The planning fence is closer than the demand fence.
   This statement is false. Typically, the demand fence is closer to the current date than the planning fence. The demand fence is where demand is firm and changes are less likely, while the planning fence is further out and allows for more flexibility in planning.

In summary, the first statement is true, and the others have varying degrees of accuracy based on context and specific organizational practices.