Explanation:

Task swapping is a method used in multitasking operating systems to allow multiple tasks or processes to run concurrently on a single processor. It involves the process of temporarily suspending the execution of one task and resuming the execution of another task.

Regular periodic point:
In the context of task swapping, a regular periodic point refers to a specific point or interval in time when a task is scheduled to be swapped out and another task is scheduled to be swapped in. This interval is typically determined by the scheduling algorithm used by the operating system.

Options:
Let's examine each option and determine whether it works in a regular periodic point or not.

a) Pre-emption:
Pre-emption refers to the act of forcibly interrupting the execution of a task in order to allow another task to run. This method does not work in a regular periodic point because it does not follow a predefined schedule. Instead, it allows tasks to be interrupted at any point in time.

b) Time slice:
Time slicing is a method of task scheduling that divides the available processor time into small time intervals called time slices. Each task is allocated a time slice during which it can execute before being swapped out. This method works in a regular periodic point because the tasks are scheduled to be swapped out and swapped in at specific time intervals.

c) Schedule algorithm:
A scheduling algorithm is responsible for determining the order and timing of task execution. While a scheduling algorithm plays a crucial role in task swapping, it is not a method of task swapping itself. Therefore, it does not work in a regular periodic point.

d) Cooperative multitasking:
Cooperative multitasking relies on tasks voluntarily yielding control to other tasks. It does not involve the forced pre-emption of tasks. This method does not work in a regular periodic point because it relies on the cooperation of tasks rather than following a predefined schedule.

Conclusion:
Based on the explanations above, the correct answer is option 'b) Time slice' because it involves dividing the available processor time into specific time intervals during which tasks are swapped in and out, making it suitable for regular periodic points.