Which of the following is the first step when defining a scientific problem? A) Conducting experiments to test hypotheses. B) Reviewing existing scientific literature. C) Posing questions about the natural world based on observations. D) Collecting data using measurement tools.

The correct answer is C) Posing questions about the natural world based on observations.<br /><br />When defining a scientific problem, the first step is to pose questions about the natural world based on observations. This involves identifying and formulating a specific question or problem that can be investigated through scientific methods. The other options, such as conducting experiments, reviewing existing literature, and collecting data, are subsequent steps that follow the initial formulation of the problem.