In descriptive scientific investigations, scientists often make observations to understand the interacting parts of a complex

The correct answer will be- complex system.

Explanation:

A scientific investigation is performed to understand and explain the natural phenomenon using the scientific method.

An investigation is performed in one of the three ways: descriptive, comparative and experimental.

In the descriptive investigation, the investigation provides a descriptive account of any "complex system" by observing it when no prior knowledge is known. Therefore this method does not include the formation of a hypothesis.

Thus, complex system is the correct answer.

In descriptive scientific investigations, scientists often make observations to understand the interacting parts of a complex SYSTEM.