The task here is to identify which factors are crucial in the formulation of a research problem. Let's break down each component given in the options:

1. Object behind the researcher's choice: The purpose behind the selection of a research topic is critical. It determines the direction and the importance of the research. Knowing why a topic is chosen helps in formulating relevant questions and hypotheses.
2. Specific questions: Detailed and specific questions help in narrowing down the research problem. They also assist in focusing the study on particular aspects that need exploration, making them indispensable when formulating a research problem.
3. Conceptual model: A conceptual framework is essential as it outlines the possible relationships between variables and constructs of the study. This model provides a theoretical basis and helps in developing a structured approach to the research problem.
4. Negative factors: While considering negative factors is important for risk assessment, they do not directly contribute to formulating the research problem. Instead, they serve to identify potential challenges or limitations.
5. Reasons for unlimiting the study: Unlimiting the scope does not directly help in formulating a research problem. Instead, it refers to broadening the scope, which can make the study less focused.
6. Construction of hypotheses: Hypotheses are conjectures that need to be tested within the research. Constructing hypotheses is directly linked to the research problem as they emerge from the problem being studied.

From this analysis, the correct formulation of a research problem would certainly involve:

• (a) Object behind the researcher's choice
• (b) Specific questions
• (c) Conceptual model
• (f) Construction of hypotheses

Therefore, the correct answer is (a), (b), (c) and (f), as these elements comprehensively contribute to developing and defining a research problem.