The correct answer is option 'C': Determining information needs.

Explanation:
An MIS (Management Information System) is a computer-based system that provides managers with the tools and information they need to effectively manage an organization. It helps in the decision-making process by providing timely, accurate, and relevant information.

Determining information needs is the first necessary step to effectively operate an MIS. This is because before any information can be collected, analyzed, or summarized, it is important to identify the specific information needs of the manager. Without a clear understanding of what information is required, the MIS will not be able to provide the necessary support for decision-making.

Here is a detailed explanation of why determining information needs is the first necessary step in operating an MIS:

1. Identify the manager's role and responsibilities:
- Understanding the manager's role and responsibilities is essential to determine the type of information needed. Different managers have different information requirements based on their area of responsibility and level of authority.

2. Define the decision-making process:
- Managers make decisions at various levels, ranging from strategic decisions to operational decisions. Each decision requires specific information to support it. By defining the decision-making process, the information needs can be identified accordingly.

3. Determine the objectives of the organization:
- The objectives of the organization play a crucial role in determining the information needs. The MIS should provide information that aligns with the organization's goals and objectives.

4. Identify the key performance indicators (KPIs):
- Key performance indicators are the measurable values that indicate how effectively an organization is achieving its objectives. By identifying the KPIs, the information needed to measure and monitor performance can be determined.

5. Assess the current information system:
- Evaluating the existing information system helps identify any gaps or deficiencies in meeting the manager's information needs. This assessment provides insights into the areas where the MIS can be improved.

Once the information needs are determined, the MIS can be designed and implemented to collect, store, process, and deliver the required information to the manager in a timely and efficient manner. The subsequent steps of summarizing data, analyzing data, and gathering appropriate information can then be carried out based on the identified information needs.

In conclusion, determining information needs is the first necessary step in operating an MIS as it sets the foundation for designing and implementing an effective system that supports the manager in discharging their managerial functions efficiently.