The frequency of the control process involves the following:

Concurrent, constant and periodic control

Concurrent, constant and observational control

Constant, periodic and post-control

Constant, periodic and occasional control

None of the above

None of the above

The correct answer is: Concurrent, constant and periodic control.

To determine the correct answer, let's break down the three terms mentioned: concurrent, constant, and periodic control.

1. Concurrent control: This involves monitoring and adjusting activities as they happen in real-time. It enables immediate detection and correction of any issues. Examples of concurrent control include supervision, surveillance, and real-time feedback.

2. Constant control: This refers to maintaining a consistent level of control over time. It ensures that standards and processes are consistently followed, preventing deviations and maintaining stability.

3. Periodic control: This involves conducting control activities at regular intervals or specific time periods. It typically involves reviewing performance data, conducting audits, and evaluating outcomes periodically.

Analyzing the provided options:

A. Concurrent, constant, and periodic control: This option includes all three mentioned terms and seems to cover the full range of control processes.

B. Concurrent, constant, and observational control: Although concurrent and constant control are covered in this option, observational control is not mentioned. Observational control typically refers to assessing and monitoring activities without immediate intervention, which is not the same as concurrent control.

C. Constant, periodic, and post-control: This option includes constant and periodic control but adds "post-control," which is not a commonly used control term. Therefore, this option is not accurate.

D. Constant, periodic, and occasional control: Similar to the previous option, this includes constant and periodic control but adds "occasional control," which is not a standard control term. Thus, this option is not correct.

Based on this analysis, the correct answer is A. Concurrent, constant, and periodic control.