The correct answer is: A. Part of managerial accounting.
Cost accounting is a branch of accounting that focuses on the measurement, analysis, and reporting of costs. It is used by managers to make decisions about pricing, production, and other aspects of running a business.
Financial accounting, on the other hand, is a branch of accounting that focuses on the preparation of financial statements for external users, such as investors and creditors. It is not concerned with the measurement and analysis of costs.
Liability accounting is a branch of accounting that focuses on the measurement and reporting of liabilities. It is not concerned with the measurement and analysis of costs.
In conclusion, cost accounting is a part of managerial accounting, not financial accounting or liability accounting.