According to the PMBOK® Guide (Project Management Body of Knowledge), specifically within the Project Quality Management knowledge area, various tools and techniques are used to plan, manage, and control quality.

Flowcharts (Option C): These are also referred to as process maps because they display the sequence of steps and the branching possibilities that exist for a process that transforms one or more inputs into one or more outputs. Flowcharts are specifically noted in the PMI standards for their utility in understanding and estimating the cost of quality in a process. This is because they show where potential failures can occur or where quality checks are needed, allowing the team to visualize the relationship between process steps and identify where rework or inspection costs (Internal/External Failure costs) might accumulate.

Checksheets (Option A): Also known as tally sheets, these are used to organize data during the collection process. While they help identify defects, they do not provide the process-wide visualization needed to estimate the total cost of quality.

Histograms (Option B): These are bar charts that show the graphical representation of numerical data, often used to show the frequency of defects or the central tendency of a data set. They describe the state of the data but not the flow of the process.

Control Charts (Option D): These are used to determine whether or not a process is stable or has predictable performance. They monitor process variance over time but are not primarily used for initial cost estimation of the quality process itself.

In the PMI framework, the Cost of Quality (COQ) includes all costs incurred over the life of the product by investment in preventing nonconformance to requirements. Flowcharts help identify these investment points (Prevention and Appraisal) versus the potential failure points.