When a system of classification is based on observation of a predetermined set of factors, it is called:

a subjective system
a natural system
an artificial system
an objective system

an objective system

When a system of classification is based on observation of a predetermined set of factors, it is called an objective system.

When trying to determine the answer to this question, it's important to understand the definitions of the terms given as options. Let's break them down:

1. Subjective system: This refers to a system that is influenced by personal opinions, biases, or interpretations. It means that the classification is based on individual perspectives rather than objective criteria.

2. Natural system: This term refers to a system of classification that is based on the inherent characteristics or attributes of the objects being classified. It means that the classification is derived from nature or the natural state of the objects.

3. Artificial system: This term refers to a system of classification that is artificially created or imposed by humans. It means that the classification is not inherent or natural, but rather a product of human design and preferences.

4. Objective system: This refers to a system of classification that is based on factual and measurable criteria. It means that the classification is not influenced by personal opinions or interpretations but is solely determined by objectively observable factors.

Given the definitions provided, the correct answer to the question is an "objective system." When a system of classification is based on the observation of a predetermined set of factors, such as factual and measurable criteria, it is considered an objective system. This means that the classification is not influenced by personal opinions or interpretations but rather determined by the objective observation of specific factors.