Here's why:

* Experiments: These are controlled procedures designed to test a specific hypothesis. They involve manipulating variables and measuring the results.

* Observations: These are careful and systematic recordings of phenomena. While not always as structured as experiments, observations can provide valuable data to support or refute a hypothesis.

Here's how the other options relate:

* Scientific Principles: These are well-established and widely accepted explanations of natural phenomena. They are often derived from numerous experiments and observations. While they can be used to guide hypotheses, they are not tools for directly testing them.

* Theories: These are broad explanations for a wide range of phenomena, supported by a large body of evidence. They can be used to generate hypotheses, but like principles, they are not directly used for testing them.

In summary: Experiments and observations are the tools used to gather data and directly test a hypothesis. Scientific principles and theories provide context and background knowledge for formulating hypotheses.