Final answer:
In the context of back-office functions, purchasing, and accounting are both examples of essential internal operational tasks that support a company's infrastructure and financial management.
Step-by-step explanation:
Back-office functions are the parts of a company's operations that are not seen by customers, but which are essential for the running of the business. Examples of back-office functions include C. purchasing and D. accounting. These activities are integral to maintaining the business's infrastructure, ensuring that transactions are recorded accurately, and managing the company’s financial affairs. Tasks such as purchasing include procurement of goods and services that the company requires to operate, while accounting involves tracking income and expenditures, processing payroll, and preparing financial reports. Both are classic examples of back-office work, distinct from customer-facing roles or supplier interfacing.